The Latest In All Natural Preservatives, and the Truth (Part III)

Are there any natural and safe preservatives to use?

Since publishing part I and part II of this series, I’ve had an overwhelming response for wanting to know when part III would be out. It took longer than expected as there are thousands of chemicals out there, and safety data for only a few. But safety alone is not enough. What’s the point of adding an ingredient if it doesn’t do the job it was intended to do? So research had to be done twice, once for safety, and once for efficacy.

Now that we covered what some of the basic chemicals are in part I, and what the fancy new mixed chemicals with fancy new names are in part II, it’s time to discuss some of the ingredients that are commonly believed to be safe to use. I’ll share the studies with you that show which preservatives have shown they can be safe. I say “can be” not “are” safe, because there are still the following considerations:

1. Final amount used – things can be safe at lower concentrations but not in higher concentrations.

2. Interactions with other ingredients – sometimes two compounds can react and form a third.

3. pH – Many compounds will lower/raise pH making the product unsafe to use. Alternately, some compounds will be effective at certain pH levels, but not at others.

4. Other ingredients – Just because I list something here, doesn’t mean that it automatically will behave like chemical preservatives commonly found in personal care products. I am merely providing a list of natural preservatives that studies show are both effective, and non-toxic at proper concentrations. How these are used can change things drastically, so use appropriately with caution.

5. Essential oil oxidation is never talked about but should be. Once essential oils began to oxidize, many can turn into something toxic. Proper handling, storage, and formula mixture should be considered.

6. There is also the issue of purity of essential oils. Where one orders their oils from makes a difference. Essential oils can sometimes be contaminated with toxic byproducts of processing – depending on how the oils are produced or purified. Many essential oils are cut with other oils in an effort to reduce production costs, or simply because pure essential oils are not stable to be stored without a carrier oil.

First, and very importantly, some more disclaimers.

Different people have different allergies and sensitivities. Just because something has been supported as safe in lab experiments, doesn’t mean an individual isn’t going to have a reaction. A person can be allergic to anything. I have formulated products for customers that are allergic to common things like food dyes, and uncommon things like beeswax. The fact of the matter remains, that there is no such thing as a perfect product. Every human body is different, and they will have different reactions to a specific product, which is why there is a need for so many different products out there. This is also why it’s important to disclose all ingredients if you’re selling products to others: so you don’t cause someone to have an adverse reaction. Some allergic reactions can be deadly.


There is a reason that major manufacturers use the soup of chemicals that they do. Consumers have come to have a certain expectation about their products. Purchase from your favorite vendor, apply the product, and have the perfect feel and consistency every time. A perfect product per se. But for that product to be consistent after shipping then sitting on a shelf for six months to a year, this is where the chemicals come in. Manufacturers fill the jars with chemicals to keep products from separating, oxidizing, and most importantly, spoiling due to bacteria and fungus. Then there’s one more very important aspect to this: the cost of this needs to stay minimal. When you put all this together, you discover that this has been turned into an art, not exactly a science.

Rather than using ingredients that are safe, but cost more and require re-formulations, major manufacturers use standard tested recipes, only changing the formulas around the margins using a dab of this, and a dab of that. This creates the superficial appearance that they are different from each other. But the rest of the ingredients still follow typical chemical soup recipes to make the product appear and smell like it is actually good for your skin, when in fact it’s not. Instead of spending money on better quality ingredients, the money is spent on marketing to fool the average consumer into thinking that the brand actually cares about them, when in fact, they do not. Or that money is used to pay celebrities to endorse the product. Such products are designed to be able to sit on a shelf for long periods of time, while maintaining all the characteristics of how the product is intended to behave, not what the product is supposed to do for the body. Sadly, this results in most people having a certain unrealistic expectation of the products they purchase.

This contrived expectation is difficult to meet with all natural ingredients. Which is why so many of your favorite all natural brands eventually throw in the towel, and add the chemicals to their products to meet those expectations.


There is something to be said about product safety, as products do expire. Mold and bacteria will find their way in, and will multiply, and can be potentially harmful. The easiest way to deal with this problem is to use toxic chemicals that inhibit growth of these microorganisms. But one has to remember, that our skin is alive, and chances are if something is toxic to bacteria and fungus, it may also be toxic to not just our skin, but the rest of the body. Our skin is permeable, particularly to smaller molecules and lipid soluble molecules, meaning that chemicals can enter your bloodstream through the skin. It may seem like a conundrum at first, because it appears that you have no choice but to use toxic chemicals to prevent your product from spoiling, yet those same chemicals are also bad for you. But this does not have to be the case. The real answer is three parts:

1. Prevent any bacteria/mold from being in the product in the first place, by sterilizing everything used to put in the product, including the jar itself, and keeping the production environment sterile. If you’re a home based business, you may consider investing in a fume hood to maintain a sterile environment, such as this one (pd link) 24″ wide fume hood. This is what is usually found in labs for any project that requires a sterile environment.

2. Re-formulate using natural preservatives that are not harmful (or are at least less harmful), than some of the standard chemicals. More on this shortly.

3. Use proper storage conditions, such as refrigerating your product and teaching your consumers about proper storage conditions for their all natural products. At first I had a lot of complaints from customers who said they didn’t like going to the kitchen to get their face cream, but the complaints reduced when I started recommending putting a mini refrigerator in their bathroom, such as this (pd link) 15 Liter Compact fridge.

The Pink Elephant in the Room

As you have probably noticed, a huge problem has already appeared, and I haven’t even mentioned ingredients. There is a huge cost associated with proper equipment, storage, and even a larger cost with formulating a product.

I know the amount of time and research it takes to formulate one product. When using natural preservatives, you can’t apply the same principles to all products like you can with most of the chemical preservatives. You have to formulate according to the specific product, and include variations such as consistency, pH, application, and many other factors. This is why major manufacturers don’t bother reformulating. It takes too much time, costs too much money, and the consumer hasn’t shown this to be a priority to them. So they use cookie cutter formulas like those found here, and spend millions on advertising instead. They fool the consumer that their products are safe, and there are no regulations or laws to stop this.

It’s Possible!

Formulating real natural products is not impossible if one is willing to take the time. There are natural preservatives that can be used. Below is a list of some of them. I have included research that I could find to back these statements. While these are not as simple of a solution as just putting in 0.2% of chemical X, this does show you that toxic chemicals are not necessary in our personal care products, and we can have not only clean healthy products for our bodies, but safe products as well. For us and our planet.

One More Disclaimer…

As far as natural preservatives, or even just ingredients used for that matter, pH plays an important role in efficacy. One can’t just say that a certain compound, natural or otherwise, is effective in all circumstances of preserving something. For example, studies showed that in the case of using sodium acid pyrophosphate or potassium sorbate, at a pH of 5.55, both preservatives inhibited germination and growth of Clostridium botulinum (a very deadly toxin if ingested). However at a slightly higher pH of 5.85, these did not stop germination and growth.1 At the lower pH either of these might only stop or slow cell division. Bottom line: a slight difference in pH can make a big difference in the effectiveness of these as preservatives. A proper (calibrated) pH meter is the only way to measure pH accurately enough to be safe.

The human skin serves as a barrier; it protects us from invaders that would otherwise harm us such as bacteria and fungus. It also helps to serve as a layer of protection from the sun (UV light is damaging), and other natural exposures that could harm us, such as water (which could dilute our cells without our skin), and even the air (which can cause desiccation and oxidation). So why is pH important? Because if the product you make results in a pH that is too low, or too high, you will harm your skin. It could result in more photo-sensitivity, which can lead to burns. Or if the pH is extreme in either direction, you can literally cause a chemical burn on your skin. pH matters, and investing in a proper tool to measure pH is not only wise, but necessary. This is especially true if you are formulating your own creams that do not have the pH tested, such as recipes found on popular websites. You want the final pH to be between 5.0 and 5.5 for best prevention and treatment of skin diseases like irritant contact dermatitis, atopic dermatitis, ichthyosis, acne vulgaris and Candida albicans infection.2

If you are planning on selling your creams, then I can’t stress the importance of proper pH enough. It would be wise to invest in a quality emulsion pH meter.Or even if you’re just DIY’ing your products for self use, you can spend a little less and get something like this pH pocket tester provided you don’t mind a probe that is more difficult to clean.
But make sure that you are regularly calibrating your pH meter for correct readings, and storing your pH meter in a proper buffer solution. If you’re going to invest in a pH meter, you also have to invest in proper calibration solutions, and make sure to also have proper storage solution. a pH meter is dependent on the user as much as the user is dependent on the meter. Proper calibration, along with proper storage of the pH meter when not in use, is essential in correct pH readings.
One last thing about pH. Some things, such as soap, are highly dependent on pH. If you adjust the pH of your liquid soap, then it’s no longer soap. Not to mention that at a lower pH, you must add stabilizers and preservatives to prevent bacterial/fungal growth. For certain products like soap to have a higher pH is perfectly fine, because you’re just temporarily applying it to your skin to perform a specific action, and then washing it off with water; you are not leaving it on your skin.

Disclaimers aside, and not in any particular order… some potentially safe preservatives:

If you don’t find one of your favorite preservatives on this list, you can always check to see if your favorite ingredient has GRAS (Generally Recognized As Safe) status by the FDA. See the full list here. Just remember, being on the GRAS list doesn’t mean that studies show it to be safe, it just means there’s not enough studies to show it’s not.


Potassium Sorbate

One of my favorite preservatives happens to also be used in my favorite drink: wine. Wine is made via the fermentation of the sugar from grapes, by using different yeast strains to ferment different types of grapes to make different types of wine. At the end of the process, once the sugar is all gone and the wine is complete, a common ingredient used to make sure all the yeast has died is potassium sorbate.

Potassium sorbate is a salt derived from sorbic acid and has attained GRAS status. It is used in a variety of foods as a preservative, and also in personal care products. I use it in some of the products I formulate, specifically those that have Aloe Vera in them, as that is a very difficult natural ingredient to keep from spoiling. However, it is important to note that the effectiveness of potassium sorbate is dependent on the final pH of the product. Studies show that potassium sorbate has no mutagenic effect when it is administered in an acid enviornment,3 and that it is not toxic in vivo or in vitro.4 When potassium sorbate was compared to Benzalkonium chloride in nasal sprays, potassium sorbate showed little toxicity even at increased concentrations.5

Not only does pH matter, but concentration matters as well. One study found that pre-treatment of apples on a stick with 40% solution of potassium sorbate was most effective.6 Regarding the effects of potassium sorbate on brown rot of stone fruit (post harvest), immersion of fruit into a 15 g/liter solution of potassium sorbate for 120 seconds reduced brown rot by over 80%. Cellular enzyme activity of bacteria was also reduced by 54% when treated with potassium sorbate.7

Another study looked at production of a specific fungal mycotoxin to see how effective potassium sorbate and another preservative were.8 While potassium sorbate did inhibit overall growth of the fungus, it did not inhibit production of the mycotoxin. Actually it increased production of the toxin.

While high concentrations of potassium sorbate show better efficacy, chromosomal damage can also start to occur. When WBCs (lymphocytes) were exposed to four different concentrations of potassium sorbate (48 hours at 125 mcg/ml, 250 mcg/ml, and 1000 mcg/ml), the 500 mcg/ml and 1000 mcg/ml concentrations increased the chromosomal damage, while the lower doses did not.9

When researchers used 10 times the acceptable daily intake (ADI) of four different preservatives (one of which was potassium sorbate), they did not find that such a high concentration was mutagenic, but they found they were genotoxic.10 While there is a difference between mutagenic and genotoxic, the point I’m making is that concentration matters. When it comes to potassium sorbate, using too much can become problematic.

The recommended pH for potassium sorbate is between 2 and 6.5, and the recommended concentration is 0.15-0.3% (if used alone) or 0.1-0.2% (if used in combination with other preservatives).11


Citric Acid

Another one of my favorite preservatives is Citric Acid (which also has GRAS status). But if you want non-GMO, look for the Non-GMO seal. Citric acid can be produced from natural ingredients such as lemons or limes, but is actually commonly produced by fungi.12 Those fungi are usually fed beets as a source of sugar, and those beets are likely GMO. Also, if you’re going to sell your product, you’ll need to know the source as some Vegans will not want products made from fungi. So this is one of those where you must check out your source and know what you’re actually buying.

Although citric acid was originally used inadvertently as a preservative, more studies are being done that show efficacy. One study showed that all staphylococci tested were susceptible to citrate at tested concentrations.13 Other studies have shown that dipping potatoes in a solution of ascorbic and citric acid before vacuum-packing and cooking (95°C for 50 min) inhibited growth and toxin production by proteolytic C. botulinum type B at an incubation temperature of 15°C for 70 d and at 20°C for at least 14 days.14

Studies also show that when citric acid is combined with potassium sorbate, the combination was more effective than sodium benzoate in the inactivation of ascospores in grape juice.15 And citric acid combined with caprylic acid in carrot juice is also effective against Escherichia coli O157:H7 and the endogenous microflora.16

Further studies are being done to establish efficacy of citric acid as a preservative. For example, Nisin combined with citric acid as a food preservative was demonstrated to be effective in preserving milk and may potentially address the issue of bacterial resistance.17

But combining two different potential preservatives does not always result in a synergistic effect. One particular study showed that citrate salt was active against gram-positive species and Candida albicans, but showed little activity against gram-negative species; acetate salt showed the opposite results. Yet their combination did not show synergism or antagonism.18

Citric acid might be effective at lower concentrations than ascorbic acid according to this study.19 However, if read carefully, the study can be inferred that at higher concentrations it is also not guaranteed that all the acids will be released. Citric acid is a weak acid, so higher concentration doesn’t necessarily mean that it will all dissociate. Citric acid has three potential protons that can be released, but pH will determine how many protons are actually released, which determines the amount of efficacy. This is important, because when one begins to use citric acid as a preservative, and tests the final product pH, one will see that citric acid does not produce a linear dose dependent change in pH.

So while citric acid can be used as preservative, it is not possible to offer someone a percentage to formula ratio, as there are too many variables that can occur in the final formulation.

It is VERY important to note, that pH is a factor here. Knowing the final pH of your cream will determine if your cream is both safe, and preserved. Lastly, citric acid can cause photosensitivity, so it is important it is not used in products that will be used with sun exposure and without sun protection. While I think citric acid is great, it has a lot of considerations, including pH, concentration, and photosensitivity. And don’t forget the source of the citric acid.



Who doesn’t love the smell of cinnamon? The nurse I used to work with who was terribly allergic. I actually felt bad for her as cinnamon is just so pleasant, but figured it was karma because she was such a mean nurse. All jokes aside, few people will argue against cinnamon, and it certainly is one of my favorite scents.

But is it effective as a antimicrobial? Anti-fungal? And is it safe? This section is focused on using cinnamon in tooth pastes and tooth powders. I do not recommend cinnamon on the skin.

Studies going all the way back to 1995 show cinnamon to have efficacy against food borne bacteria. Cinnamon is effective against some fungal pathogens, although cinnamon oil was more effective over just cinnamon powder.20, 21

Various studies have been conducted which include a combination of natural ingredients with cinnamon to show increased efficacy of antimicrobial activity.22, 23, 24 This sparked enough interest that studies were completed isolating cinnamon’s compounds and comparing them in effectiveness for antimicrobial activity.25 Some of the promising oils (cinnamon included) were even tested in their vapor stage for efficacy.26 Studies on the efficacy of cinnamon in modified atmosphere environment were even performed.27

There’s also a study from 2007 that reveals that cinnamon may have the potential to prevent Chaga’s disease. Sign me up. I studied Chaga’s disease in university and it’s not pretty. Perhaps I’ll add a little more cinnamon to my daily use.

There seems to be quite a bit of evidence for other health effects, especially for those with type II diabetes. Studies show that the naturally occurring compounds in Cinnamomon Cassia improve insulin sensitivity.28

There is no shortage of efficacy studies. But given that cinnamon is often added to toothpaste, which means it can be accidentally ingested while brushing one’s teeth, is it safe? I mean we cook with it, eat it all the time, scent our house with it, and it even has GRAS status. But is it safe?

One study showed a slight decrease in the kidney and liver weight of rats treated with 0.5g/kg and 2.0g/kg. Hence, these toxicity studies suggest that cinnamon aqueous extract is low to moderate in toxicity and cinnamon aqueous extract below 0.5 g/kg dose level is safe to be used in the efficacy study – especially for diabetes treatment.29

Then there is the related issue of coumarin. Cinnamon can contain up to 1% of this compound, which can be liver toxic if a sufficient amount is consumed. The relative extent of absorption of coumarin from powder of cassia cinnamon is only slightly lower than that of isolated coumarin.30 Therefore care must be taken when using cinnamon in products that can be ingested.

I found study after study in regards to cinnamon oil and it’s various uses from pesticides to mycocides and even spider killer.31

But is there such a thing as too much of a good thing?

While actual toxicity studies are few and far between, one recent study revealed that while body weights of rats were normal after receiving cinnamon extract at up to 2000 mg/kg. High-dose intake of cinnamon extract (2000 mg/kg) showed potential nephrotoxicity and hepatotoxicity to both males and females.32

This recent study explored cinnamaldehyde effects after heating and inhalation (such as when used as flavorings in e-cigarettes). Results showed that the heating portion made no difference, however, the studies did suggest that micromolar levels of cinnamaldehyde could alter cardiac excitability, in part by impairing the processes that regulate membrane potential and depolarization. (You might not be smoking it, but if you’re making products at home, and are adding cinnamon to your hot oils – just some food for thought).

My biggest interest was whether or not cinnamon commonly results in conditions such as contact dermatitis, especially when used in toothpastes. Unfortunately, studies are few that I could find. I think this may be because cinnamon is not usually considered a culprit in allergic reactions, but this could be due to the difficulty of diagnosing a cinnamon sensitivity. Perhaps the contact dermatitis isn’t as obviously figured out, as standard patch tests aren’t enough in cases of orofacial granulomatosis (persistent enlargement of the soft tissues of the mouth and lips). One study indicated that standard patch testing was much less likely to detect allergy to benzoates and cinnamon compounds (7%) than typical urticarial tests (55%).33

One study did attempt to look at the causes of allergies to (ingredients of) toothpastes. Out of 47 small case reports, and citations published between 1900 and 2016 describing more than 60 patients allergic to toothpastes, three larger analysis were not able to conclusively determine which ingredient(s) held the role of contact allergy to toothpastes in patients with oral symptoms.34

While I was not able to find studies to show toxicity from cinnamon (other than the coumarin component), I decided to take a closer look at Cinnamaldehyde, which is the organic compound that gives cinnamon it’s scent and flavor. It’s usually obtained from the oil of the cinnamon bark, so technically natural. But it can also be made from other compounds such as cinnamyl alcohol (the alcohol form of cinnamaldehyde). (The first synthesis from unrelated compounds was the aldol condensation of benzaldehyde and acetaldehyde). Might want to check if your cinnamon oil is steam distilled from cinnamon bark, or made by another process. My research was concentrated on actual cinnamon or oil derived from cinnamon.

It turns out cinnamon is not so innocent. The cinnamic aldehyde found in cinnamon is a known irritant. One study showed that workers processing cinnamon before export are exposed to much cinnamon dust. Forty such workers with an average of four years’ service in the industry were examined. Thirty five workers (87.5%) had symptoms: asthma (22.5%), irritation of skin (50%), loss of hair (37.5%), and smarting (pain) of eyes while at work (22.5%). Loss of weight (65%) was the commonest finding. Contact dermatitis which has previously been described was not found in any of the workers.35

While immediately I do not find any concerns, that doesn’t mean it’s 100% safe. Lack of safety data does not equal safety, just means we have insufficient data.

Unfortunately, in the few studies that have been done, it was difficult to decipher where the cinnamon oil was attained from, which will make a difference. Given cinnamon’s long track record of ingestion by humans, along with many studies showing efficacy against bacteria and fungus, I personally would take my chances with cinnamon over most other chemicals found out there; provided I wasn’t one of those who experienced orofacial granulomatosis.


Thymol – Thyme

I love cooking with Thyme, a relative of the Oregano genus. It’s one of my favorite spices that I add to almost everything from meats to vegetables, and especially in my homemade soups.

Thymol, which is found in the oil of thyme, doesn’t like to mix well with water, but offers antiseptic activity that used to be used by the natives as a way to treat skin infections, small wounds, and even gingivitis.36

The more research that is done on thymol and it’s constituents, specifically carvacrol (a compound usually found present in oil of oregano, thyme, pepperwort, and wild bergamot), the more interest there is for using it in natural personal care products. Specifically, studies that have evaluated the potential therapeutic uses for the treatment of disorders affecting the respiratory, nervous, and cardiovascular systems, along with other studies that show that thymol exhibits antimicrobial, antioxidant, anticarcinogenic, anti-inflammatory, and antispasmodic activities, as well as a potential as a growth enhancer and immunomodulator.37

There is a lot of research on thyme/thymol. In one study, it was revealed that thyme essential oil had larger antimicrobial inhibition zones than clove or cinnamon essential oils.38 And studies have even shown the potential for thymol to be used as an herbicide.39

But as with everything else, dosage matters. In one particular study, it was shown that at a lower concentration of 100mg/L of carvacrol and thymol (mix), the growth of E. coli was not inhibited. Only higher concentrations were effective. Treatment with a 400mg concentration of both carvacrol and thymol resulted in E. coli cells decreasing to undetectable levels after 6 hours of exposure. And at 800 mg, no growth was found after only a half hour treatment.40

Studies also show a syngergistic effect with other natural compounds. In one study, it was found that combining cinnamaldehyde with carvacrol and thymol resulted in a smaller population of Salmonella Typhimurium at lower concentrations than when treated with cinnamaldehyde, thymol, or carvacrol alone. The concentrations could be decreased from 400 mg/L (individually) to 100 mg/L when used in combination.41

One very interesting study demonstrated antagonistic potential of thymol against radiation-induced oxidative stress and lipid peroxidation, resulting in increased cell viability.42

How thymol works as an antibacterial is not yet known. But one study proposed that the primary mechanism of thymol toxicity at high doses is due to the formation of oxidizing radicals.43 Another study proposed the antibacterial effects were attributed to their ability to permeabilize and depolarize the cytoplasmic membrane.44 When you start talking about pro-oxidant radicals, and permeabilzing and depolarizing cytoplasmic membranes, those are phenomenon that can affect human cells. So are thymol and their constituents safe for use?

One study showed that the mild cytotoxic effect of carvacrol and thymol on human hepatoma or colonic cells had no DNA-damaging effect but reduced the level of DNA lesions induced in these cells by an oxidative agent and thus acted as antioxidants.45 Admittedly this seems at least partially contradictory to the previous study mentioned.

One study assessed the toxicological effects of oregano essential oil on the digestive tract, primarily the cytotoxic effects of carvacrol, thymol, and their mixture, on intestinal cells, after 24 and 48 hours of exposure. Results “indicated that carvacrol and the mixture carvacrol/thymol induced toxic effects. […] The main morphological alterations were vacuolated cytoplasm, altered organelles and finally cell death. In addition, although no cytotoxic effects were recorded for thymol at any concentration and time of exposure, structural changes evidenced cellular damage such as lipid degeneration, mitochondrial damage, nucleolar segregation and apoptosis.”46 While this one study may not be the end-all about safety, it certainly raises some concerns.

Another study showed that carvacrol and thymol significantly induced the structural and total chromosome abnormalities in bone marrow cells of rats, in concentrations as low as 10mg/kg for carvacrol and 40mg/kg for thymol.47

There are many studies to be found on thymol. One study in particular, noted that thymol demonstrated dose dependent cytotoxic effects on HL-60 cells (cancer cells) after 24 h of exposure, but did not show any cytotoxic effect in normal human PBMCs. According to the study, the cytotoxic effect of thymol on HL-60 cells appeared to be associated with induction of cell cycle arrest at sub G0/G1 phase, and apoptotic cell death based on genomic DNA fragmentation pattern.48

So perhaps adding thymol to a skin cream to prevent mold growth might not be a good idea! One study even indicates the possibility of increasing the permeability of skin. This study in particular intended to increase permeability in an effort to create a meloxicam transdermal cream. Results showed increased permeability at higher ratios of thymol to meloxicam.49

It seems that dose really matters with thymol and carvacrol. One group of researchers did a variation of studies on different cell types (human and animal), that showed different reactions of thymol and carvacrol dependent on concentration and cell type. It’s too much to try to paraphrase the study here, but you can read the studies on your own here.50

The authors of one very fascinating study suggest, based on their results, that carvacrol and thymol exhibit protective/damaging effects depending on cell resistance, concentration and time.51 And this is where I would like to end my research on thymol for now.

While thymol appears very promising in antimicrobial and anti-fungal activity, I could not find enough cyto-toxicity studies to determine it is safe, nor could I find conclusive studies to determine it is not safe.

As a side note, it is important to distinguish between ingesting something like thymol and getting it into your body through your skin. When ingested, compounds are broken down by the gut and metabolized by the liver before entering the blood stream. So there are more safety mechanisms in place. When something (like thymol or synthetic preservatives) gets into your bloodstream through the skin, those safety mechanisms are mostly bypassed, so there is different potential for harm.

Lastly, as mentioned earlier, thymol doesn’t like to mix well in water. In fact, it tends to have the best solubility in alcohol. But alcohol is rather harsh on the skin, and it turns out I’m not the first to be concerned about this. I found a study that shows that a specific emulsion of herbal extracts in alcohol (these are not specific to thyme) showed that it is actually safe on the skin.52 (But more research likely needs to be done.)

Based on the research I found, I would trust thymol as a preservative over many of the known toxic ones, though a little more research on thymol wouldn’t harm anyone.


Geranium essential oil

I found it difficult to research geranium, but only because there are over 400 species of geranium, and there’s little research that separates the different kinds.

One study suggests that germanium extract promotes hair growth in vitro and in vivo by regulating growth factors and cellular response.53

One study found that administration of the Geranium shiedeanum extract significantly reduced the adverse effect of ethanol on liver regeneration.54 Another study found that geranium essential oil may have significant potential for the development of novel anti-inflammatory drugs with improved safety profile55

One thing to consider is a study that found that cutaneous application of essential oils, especially geranium oil, can suppress the inflammatory symptoms such as neutrophil accumulation and edema.56

But is it effective against bacteria or fungi?

One study measured geranium as being second to cinnamon oil in its effectiveness against environmental strains of the bacteria Acinetobacter baumannii.57 Another study found that Geranium oil from Pelargonium graveolens (a very uncommon species) has strong activity against all of the clinical S. aureus bacteria — including multi-drug resistant strains, MRSA strains and MLSB-positive strains.58 *Note, this was one type of Geranium species, and recall there are over 400. And this is an uncommon species.

There are four major constituents in geranium. I say “major” because there are actually quite a few constituents; over 300 that I could find, but most of them are in smaller quantities. The four major constituents are citronellol at 28%, geraniol at 16%, citronellyl fomate at 10.4%, and linalool at 6.45%. In topical applications for insectitdal activity, cironellol and geraniol were the most potent. Linalool and citronellyl were less toxic – when isolating them individually. Geranium essential oil as a whole is less toxic than many of the individual constituents. However, removal of any of the four constituents decreased antimicrobial effectiveness, with citronellol removal producing the greatest change.59

Whenever you have a compound that is toxic to another living organism, including insects, you have to ask yourself if it is also toxic to humans. Insects and humans may be very different, but we use many of the same biological pathways on the cellular and molecular level.

One study of geranium macrorrhizum extract indicated both anti-oxidant and pro-oxidant action, presumably due to the formation of quinoidal products. The study also found that geranium macrorrhizum extracts are also abundant in quercetin-derived components.60 Quercetin is a flavanol found in many foods, which has been found to have many biological effects, including antioxidant activity.

I have kept geranium on this list because I couldn’t find enough toxicity data to remove it, and also because each ingredient takes days to research and I’d hate for all this research to not be shared. But there is still an issue with using it, due to the large number of species of geranium and the great number of constituents that make up geranium oil. Some of these may have very useful and beneficial effects, but many others may have concerning toxic effects. While smaller concentrations of toxic constituents might go unnoticed, if using something daily, these could build up. To properly evaluate all of these species and constituents would require extensive additional research. I personally do not have the time (or funding) to research all those constituents nor do I have time to review each species. For these reasons, I have delayed the choice to use geranium essential oil in any of my products, but am certainly considering it based on the information I’ve so far found.



I know few people who do not enjoy the woody perennial scent of rosemary. But it seems that few people know that rosemary is actually a member of the mint Lamiaceae family, or that it’s considered an invasive species in some parts of the world. But then cats are also considered an invasive species in some parts of the world, and there’s no shortage of cat loving people.

Rosemary has many uses. One of my favorites is keeping it in the garden among my other plants, as rosemary has shown to repel spider mites.61

Rosemary contains a number of phytochemicals, including rosmarinic acid, camphor, caffeic acid, ursolic acid, betulinic acid, carnosic acid, and carnosol. Rosemary essential oil contains 10–20% camphor.62 With such a combination of constituents, it’s no wonder there are so many successful studies showing rosemary to be both an antimicrobial and antifungal. However, it’s important to note that studies suggest that the effectiveness of rosemary oil is a consequence of the combined (and possibly synergistic) effects of several constituents, with no individual constituent making a dominating contribution.63

Not only is rosemary perfect for the garden, but it is also great in meals, and in your personal care products. Studies suggest that the extract of rosemary exhibits a protective effect against oxidative damage to DNA as a consequence of scavenging of both OH radicals and singlet oxygen.64 Rosemary is even being studied for potential inhibition of human cancer cell lines. One study showed rosemary extract is a potential candidate to be included in the anti-cancer diet with pre-determined doses to avoid toxicity.65

There are so many studies on rosemary it is truly overwhelming. So I tried to focus on efficacy studies as a antibacterial and antifungal, and on cytotoxicity. In short, studies show that rosemary is an effective antimicrobial against all gram positive and gram negative bacteria.66 Rosemary works as an antibacterial by affecting the mitotic phase, and at a concentration of 5 mg/ml completely inhibited the germination of Triticum vulgare.67

With such amazing versatility in helping humans thrive, it can’t be bad for humans right?

Again, it appears that concentration/dosage along with type of application is key. Studies show that at 24 hours post oral feeding of rosemary oil to Swiss mice with concentrations of 300, 1000, or 2000 mg/kg, all three doses of rosemary oil induced significant increases in DNA damage in the mouse cells. At 1000 or 2000 mg/kg there was a significant increase in micronucleated cells and chromosome aberrations. Based on that it can be concluded that rosemary essential oil provokes genotoxic and mutagenic effects when administered orally at such high doses.68 But I must put this in perspective. You would have to eat a lot of rosemary to match these lab results. Let’s say a person weighs 150lbs; convert that to kilograms, and that is about 68 kilograms. Even at the low dosage of 300 mg/kg, you’re looking at 20.4 grams of rosemary essential oil. 20.4 grams is about 4.78 teaspoons of rosemary oil. Almost 16 teaspoons of rosemary oil for the 1000 mg/kg dosage, and a whopping 32 teaspoons of rosemary oil to match the 2000 mg/kg dosage. This attests to the common idea that almost anything can become toxic at a high enough concentration.

One of the issues I’ve heard over and over is that rosemary prevented proper gestation during pregnancy. Apparently I wasn’t the only one who heard about this, as studies were completed to try to support this idea. In rat studies, when treated with rosemary aqueous extract at a dose level of 291.2 mg and 582.4 mg/kg of body weight for five days, body and organ weights, sperm production and food consumption were not significantly altered at the lower dose administration, nor did it interfere with gamete production. However, animals treated with the higher dose (582.4 mg/Kg of body weight) showed significant weight increase of the seminal vesicle but no significant alteration of the other variables. This suggests that rosemary extract may present an anti-fertilization effect without interfering with the normal development of the concept after implantation.69 Further studies show that when a higher dose (968 mg/Kg) was fed to rats, rosemary essential oil reduced the fetus’ body weight and induced anemia in the dams. 70 For perspective, 968 mg/Kg is not quite the 1000 mg/Kg as noted above, so not quite 32 teaspoons of rosemary essential oil. I’m not sure that I could eat 32 teaspoons of anything so concentrated.

Unless new research comes out to show rosemary as toxic at much lower concentrations, it’s staying in my product line.



When it comes to the smell of patchouli, you either love it or you hate it. There is usually no in between. And if you hate it, you don’t want to be in my lab when I make my patchouli oatmeal soap, because even with a mask on, the scent is overpowering. Don’t get me wrong, I like patchouli – in SMALL doses.

Like rosemary, patchouli is also a member of the mint Lamiaceae family. And like rosemary, there is no shortage of antimicrobial and antifungal studies. But patchouli offers much more. Studies indicate that patchouli should be considered as a potential source of anti-influenza agents for the pharmaceutical industry, as it showed protection from influenza in the mouse model against the viral infection, at a dose of 5 mg/kg/day.71 And studies show potential as a termiticide.72

But is it safe? Unfortunately I was not able to find any studies that offered a safety evaluation based on concentration/dosage. The only study I could find was terribly translated from Mandarin (I think). The study also seemed to be based on IV administration and not oral or topical, which is very different and will result in different results.

For now, until further studies show otherwise, patchouli stays on my safe list, in small doses of course.


Bee Propolis

Propolis is supposed to be effective in protecting the hive, offering both antibacterial and antifungal properties. There’s even a study that proposes adding propolis as a natural additive to orange juice.

Recent research shows a paradigm shift in how bees use propolis. It used to be believed that propolis had antibacterial and antifungal properties, which was believed to be why bees manufactured and used it. But recent research shows that bees use it more as an entombing compound. Kind of like finding an ant colony in your backyard, and building a cement building over it to prevent it from going anywhere.

But propolis does also have some antimicrobial properties. One study showed that a 4% water extract concentration produced more than 50% inhibition against all tested microorganisms.73 However, it is important to note that not all propolis is the same. Studies have found that the antimicrobial activity of propolis varies depending on the particular sample, dosage, and the extraction solvents used. Antimicrobial activity of all propolis samples increased with increasing dosage without reaching a plateau at the highest dosage tested.74

It is important to note that propolis will vary according to the bee colony. Meaning that different bees will make propolis with slightly different constituents in one geographic area compared to another, based on what is available to them. It’s like building a house in different parts of the world. Some places offer oak trees to build from, while others offer juniper tress. Bees, unlike humans, do not have home depot’s to purchase their product of choice.

Whether propolis or even beeswax is safe is not a question that can easily be answered with scientific studies. And that is because bees will fly where there is food, and bee keepers have little control over what ends up in the resulting propolis and beeswax.

What many people don’t realize when they make their own products from locally produced beeswax, is that because it’s fresh and minimally processed, there is already propolis in the beeswax. In contrast, the beeswax you buy from the store has been processed, bleached, and had all kinds of questionable things done to it. You can read more about that here. The advantage of buying local beeswax is that you know what you’re getting – or you can at least ask questions and see the bees; unlike what you buy at the store, where it’s been processed and bleached. The bad part about locally produced beeswax is you might inadvertently be getting pesticide residue in your beeswax as well.75

Contaminants are another issue. Contamination can arise from beekeeping practices or from the environment. Environmental contaminants in beeswax can include the heavy metals lead, cadmium and mercury, radioactive isotopes, organic pollutants, pesticides (insecticides, fungicides, herbicides and bactericides), pathogenic bacteria and genetically modified organisms, and the contaminants from beekeeping itself. The main contaminants are acaricides used for the control of bee brood diseases. These include lipophylic synthetic compounds and non-toxic substances such as organic acids and components of essential oils; and antibiotics including tetracyclines, streptomycine, sulfonamides and chloramphenicol. Other substances used in beekeeping play a minor role: para-dichlorobenzene, used for the control of wax moth and chemical repellents.76

These are all things to consider before choosing a beeswax or propolis source. I couldn’t find any studies that showed pure propolis to be cytotoxic, but finding a pure source of propolis/beeswax takes a lot of leg work, lots of questions to the beekeeper, and being constantly vigilant about your source of propolis and/or beeswax.


Vitamin E – AKA Alpha tocopherol

Vitamin E sounds natural and innocent enough, but I must first clarify which vitamin E to which I will be referring, and that is Alpha tocopherol, usually abbreviated as α-Tocopherol. The type of vitamin E does make a difference.

Natural vitamin E is generally labelled d-alpha tocopherol, d-alpha tocopherol acetate, or d-alpha tocopherol succinate but can sometimes appear as mixed tocopherols (mixed tocopherols contain not only d-alpha tocopherol but natural mixtures of beta, gamma, and delta tocopherols), and are derived from plants. In contrast, synthetic forms of vitamine E are labeled with a dl-prefix and are derived from petroleum products.

In the case of natural versus synthetic, when it comes to vitamin E, studies show that natural is better.77 Not to mention that synthetic vitamin E is generally derived from petroleum products, which we don’t use in our products here at Nature’s Complement.

However, Vitamin E is not listed here are a preservative, but rather as an antioxidant to keep the final product fresh. Studies show that vitamin E oil helps to prevent rancidity in oils, and is used extensively in foods, especially meats, to help prevent rancidity.

Tocopherals in general have GRAS status, but you must be careful of the source. Many Vitamin E products, even natural ones, are made from soybeans, and majority of soybeans are now GMO. It is important when choosing your Vitamin E oil that you read the label carefully, look for an d-alpha tocopherol that is non-GMO verified.


Tea Tree Oil

Tea tree oil or Melaleuca oil, known by it’s scientific name of Melaleuca alternifolia has been touted in the natural community as an anti-microbial, anti-fungal, and many claim it has anti-itch properties. I personally enjoy the herbal scent that is unique to only Tea Tree Oil.

Tea Tree oil has had some controversy in regards to use as an acne treatment. But studies showed that at a 5% concentration, it was more effective than a placebo group.78,79 Tea tree oil has also become a candidate for research against scabies with the increasing drug resistance to drugs like ivermectin. Studies also show that at 5% it was effective in comparison to other common drugs 80,81

There are a variety of studies to show that the essential oil from M. alternifolia inhibited strongly the growth of different types of microorganisms including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Penicillium italicum Wehmer, and Penicillium digitatum Sac”. 82,83

How Tea Tree works as an antimicrobial is that tea tree contains a monterpene called terpinene-4-ol. Various other compounds have been researched, but studies have identified the terpinene-4-ol as the compound that is responsible for it’s antimicrobial activity.84 It disrupts the cell membrane structure of microbes and increases the microbial membrane permeability. 85

But given how well it kills bacterial and even scabid cells, does that also mean it can harm human cells?

Given that Tea Tree oil is a mixture of over a 100 compounds, it is actually not known if it is actually safe. There have been some issues from ingestion of the oil in large amounts, such as in the case of the person who ingested half a cup of this oil which resulted in the person being comatose for 12 hours with another 36 hour of semi consciousness. However in this case the purity of the oils was not known.86

Fortunately, regulations require that the oil have a certain percentage of the compound that is known to be effective against microbials, and minimal percentage of the compounds that are known to be more toxic (at least 30% of the terpinene-4-ol and must not contain more than 15% 1,8-cineole).

In trying to review the toxicological data for tea tree oil, there was limited data. What I found was a summary written in 2005 which basically said that while relatively limited data are available on the safety and toxicity of tea tree oil, anecdotal evidence from almost 80 years of use suggests that the topical use of the oil is relatively safe, and that adverse events are minor, self-limiting and occasional. Published data indicate that tea tree oil can cause skin irritation at higher concentrations. Allergic reactions can occur as with anything, but is believed to be due to the various oxidation products that are formed by exposure of the oil to light and/or air. Data from individual components suggest that tea tree has the potential to be developmentally toxic if ingested at higher dose, however, it’s not genotoxic. 87

So basically what we have to go on (scientifically) is that people have been using it for at least 80 years, and no one has died even with ingesting half a cup of it, therefore we should assume it’s safe. That’s not a great way to evaluate for safety.

I couldn’t accept that so I kept searching. Finally I found a recent study that questions the idea that tea tree oil only targets microbial and fungal cells, and not human cells. While this study was done on swine spermatozoa and not human cells, it was an important study. It implied that more research should be done, but also showed results that at 0.6 mg/mL, the spermatozoa were not affected but that at higher concentrations this EO caused increasing impairment in a concentration-dependent manner. 88

Another recent study showed that tea tree oil fed to poultry actually had some positive effects in controlling ticks when poultry houses were sprayed with the oil, and when fed to hens it decreased morbidity.

So is tea tree oil safe? More studies need to be done. Until more research is available, I personally will never use it topically in concentrations higher than the 0.6 mg/mL, and I certainly recommend against ingesting it (we’re not chickens). But as an antimicrobial and antifungal, it seems to do the job. Just be aware of the concentration being used.

That’s Not All Folks

This is a much shorter list than I intended when I began my part III series. I have a very long list of other ingredients which I have researched but which I have not yet written in a readable format. As you can see, this is a time consuming task, and takes months to put together. Because I have had such a large number of requests for this article, I decided to post what I have gathered so far, with the intent to continue the research (and writing) and post my results as time permits. So more ingredients will be reviewed in the future.

Sign up for our newsletter to receive updates of when we post new research articles. We will continue to post information to include the references on safety and toxicology data that we find and evlauate.

For Health,



1 Wagner MK, Busta FF. Influence of a Minimal Change in pH on Germination of Clostridium botulinum 52A in Media Containing Sodium Acid Pyrophosphate and Potassium Sorbate. J Food Prot. 1985;48(8):693-696.

2Schmid-Wendtner, M.-H., and H.C. Korting. “The PH of the Skin Surface and Its Impact on the Barrier Function.” Skin Pharmacology and Physiology, vol. 19, no. 6, 2006, pp. 296–302, 10.1159/000094670.

3Budayová E. Effects of sodium nitrite and potassium sorbate on in vitro cultured mammalian cells. Neoplasma. 1985;32(3):341-50

4Jung R, Cojocel C, Müller W, Böttger D, Lück E. Evaluation of the genotoxic potential of sorbic acid and potassium sorbate. Food Chem Toxicol. 1992;30(1):1-7.

5Ho CY, Wu MC, Lan MY, Tan CT, Yang AH. In vitro effects of preservatives in nasal sprays on human nasal epithelial cells. Am J Rhinol. 2008;22(2):125-9.

6Carstens CK, Salazar JK, Bathija VM, Narula SS, Wang P, Tortorello ML. Control of Listeria monocytogenes in Caramel Apples by Use of Sticks Pretreated with Potassium Sorbate. J Food Prot. 2018;81(12):1921-1928.

7Gregori R, Borsetti F, Neri F, Mari M, Bertolini P. Effects of potassium sorbate on postharvest brown rot of stone fruit. J Food Prot. 2008;71(8):1626-31.

8Fodil S, Delgado J, Varvaro L, Yaseen T, Rodríguez A. Effect of potassium sorbate (E-202) and the antifungal PgAFP protein on Aspergillus carbonarius growth and ochratoxin A production in raisin simulating media. J Sci Food Agric. 2018;98(15):5785-5794.

9Mamur S, Yüzbaşioğlu D, Unal F, Yilmaz S. Does potassium sorbate induce genotoxic or mutagenic effects in lymphocytes?. Toxicol In Vitro. 2010;24(3):790-4.

10Abo-el-sooud K, Hashem MM, Badr YA, et al. Assessment of hepato-renal damage and genotoxicity induced by long-term exposure to five permitted food additives in rats. Environ Sci Pollut Res Int. 2018;25(26):26341-26350.

11Potassium Sorbate. Accessed 30 Nov. 2019.

12Max, Belén et al. “Biotechnological production of citric acid.” Brazilian journal of microbiology : [publication of the Brazilian Society for Microbiology] vol. 41,4 (2010): 862-75. doi:10.1590/S1517-83822010000400005.

13Lee YL, Thrupp L, Owens J, Cesario T, Shanbrom E. Bactericidal activity of citrate against Gram-positive cocci. Lett Appl Microbiol. 2001;33(5):349-51.

14Notermans S, Dufrenne J, Keybets MJH. Use of Preservatives to Delay Toxin Formation by Clostridium botulinum (Type B, Strain Okra) in Vacuum-Packed, Cooked Potatoes. J Food Prot. 1985;48(10):851-855.

15Rajashekhara E, Suresh ER, Ethiraj S. Thermal death rate of ascospores of Neosartorya fischeri ATCC 200957 in the presence of organic acids and preservatives in fruit juices. J Food Prot. 1998;61(10):1358-62.

16Kim SA, Rhee MS. Synergistic antimicrobial activity of caprylic acid in combination with citric acid against both Escherichia coli O157:H7 and indigenous microflora in carrot juice. Food Microbiol. 2015;49:166-72.

17Zhao X, Zhen Z, Wang X, Guo N. Synergy of a combination of nisin and citric acid against Staphylococcus aureus and Listeria monocytogenes. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2017;34(12):2058-2068.

18Lee YL, Cesario T, Owens J, Shanbrom E, Thrupp LD. Antibacterial activity of citrate and acetate. Nutrition. 2002;18(7-8):665-6.

19Giannuzzi L, Zaritzky NE. Chemical Preservatives Action on Microbial Growth in a Model System of Refrigerated Prepeeled Potatoes. J Food Prot. 1993;56(9):801-807.

20Sep 2, 2008 … almost all of the food-borne microbes. B. cereus was found to be …. in agreement with published data (Charai et al., 1996;. Sivropoulou et al.

21Both Cinnamomum verum J.S. Presl. and Cinnamomum cassia Blume are collectively called Cortex Cinnamonmi for their medicinal cinnamon bark.

22Nov 1, 1995 … · RIGHTS & … DOI: 10.1021/acs.jmedchem. 9b00616. Xiaomei Lyu …. DOI: 10.1021/jf000263c. Mendel …

23 0.99% … 19. http:// 0.39%. 20. 0.36%. 21. abs/10.1021/am507532p …..

24 Food Research International. Volume 48, Issue 2, October 2012, Pages 777-783.

25 Food and Chemical Toxicology. Volume 45, Issue 9, September 2007, Pages 1650-1661

26Antimicrobial activity in the vapour phase of a combination of cinnamon and clove essential oils. Food Chemistry Volume 116, Issue 4, 15 October 2009, Pages 982-989.

27Antimicrobial activity of cinnamon and clove oils under modified atmosphere conditions. International Journal of Food Microbiology. Volume 107, Issue 2, 15 March 2006, Pages 180-185.

28Chromium and Polyphenols from Cinnamon Improve Insulin … Accessed 30 Nov. 2019.

29’’Hyperchromic’’ and ’’hypochromic’’ Effects. (a) Hyperchromism Has … Accessed 30 Nov. 2019.

30Relative bioavailability of coumarin from cinnamon and cinnamon‐containing foods compared to isolated coumarin: A four‐way crossover study in human volunteers. Molecular Nutrition Food Research. Volume55, Issue4. April 2011. Pages 644-653.


32Yun JW, You JR, Kim YS, et al. In vitro and in vivo safety studies of cinnamon extract (Cinnamomum cassia) on general and genetic toxicology. Regul Toxicol Pharmacol. 2018;95:115-123.

33Fitzpatrick L, Healy CM, Mccartan BE, Flint SR, Mccreary CE, Rogers S. Patch testing for food-associated allergies in orofacial granulomatosis. J Oral Pathol Med. 2011;40(1):10-3.

34De groot A. Contact Allergy to (Ingredients of) Toothpastes. Dermatitis. 2017;28(2):95-114.

35Uragoda CG. Asthma and other symptoms in cinnamon workers. Br J Ind Med. 1984;41(2):224-7.

36Wikipedia Contributors. “Thymol.” Wikipedia, Wikimedia Foundation, 22 Mar. 2019, Accessed 23 Apr. 2019.

37Salehi B, Mishra AP, Shukla I, et al. Thymol, thyme, and other plant sources: Health and potential uses. Phytother Res. 2018;32(9):1688-1706.

38HOSSEINI, M.H., et al. “ANTIMICROBIAL, PHYSICAL AND MECHANICAL PROPERTIES OF CHITOSAN-BASED FILMS INCORPORATED WITH THYME, CLOVE AND CINNAMON ESSENTIAL OILS.” Journal of Food Processing and Preservation, vol. 33, no. 6, Dec. 2009, pp. 727–743, 10.1111/j.1745-4549.2008.00307.x. Accessed 8 May 2019.

39Pinheiro, Patrícia Fontes, et al. “Phytotoxicity and Cytotoxicity of Essential Oil from Leaves of Plectranthus Amboinicus, Carvacrol, and Thymol in Plant Bioassays.” Journal of Agricultural and Food Chemistry, vol. 63, no. 41, 8 Oct. 2015, pp. 8981–8990, 10.1021/acs.jafc.5b03049. Accessed 4 Jan. 2020.

40Xu, J., et al. “The Antibacterial Mechanism of Carvacrol and Thymol AgainstEscherichia Coli.” Letters in Applied Microbiology, vol. 47, no. 3, Sept. 2008, pp. 174–179, 10.1111/j.1472-765x.2008.02407.x. Accessed 4 Jan. 2020.

41ZHOU, FENG, et al. “THE ANTIBACTERIAL EFFECT OF CINNAMALDEHYDE, THYMOL, CARVACROL AND THEIR COMBINATIONS AGAINST THE FOODBORNE PATHOGEN SALMONELLA TYPHIMURIUM.” Journal of Food Safety, vol. 27, no. 2, May 2007, pp. 124–133, 10.1111/j.1745-4565.2007.00064.x. Accessed 4 Jan. 2020

42Archana, P.R., et al. “Thymol, a Naturally Occurring Monocyclic Dietary Phenolic Compound Protects Chinese Hamster Lung Fibroblasts from Radiation-Induced Cytotoxicity.” Mutation Research/Genetic Toxicology and Environmental Mutagenesis, vol. 680, no. 1–2, Nov. 2009, pp. 70–77,, 10.1016/j.mrgentox.2009.09.010. Accessed 4 Jan. 2020.

43Satooka, Hiroki, and Isao Kubo. “Effects of Thymol on B16-F10 Melanoma Cells.” Journal of Agricultural and Food Chemistry, vol. 60, no. 10, 6 Mar. 2012, pp. 2746–2752, 10.1021/jf204525b. Accessed 4 Jan. 2020.

44Xu J, Zhou F, Ji BP, Pei RS, Xu N. The antibacterial mechanism of carvacrol and thymol against Escherichia coli. Lett Appl Microbiol. 2008;47(3):174-9.

45Slameňová, D, et al. “DNA-Protective Effects of Two Components of Essential Plant Oils Carvacrol and Thymol on Mammalian Cells Cultured in Vitro.” NEOPLASMA, vol. 54, no. 54, 2007, Accessed 4 Jan. 2020.

46Llana-Ruiz-Cabello, María, et al. “Cytotoxicity and Morphological Effects Induced by Carvacrol and Thymol on the Human Cell Line Caco-2.” Food and Chemical Toxicology, vol. 64, no. 64, Feb. 2014, pp. 281–290,, 10.1016/j.fct.2013.12.005. Accessed 4 Jan. 2020.

47Azirak, Sebile, and Eyyup Rencuzogullari. “Thein Vivogenotoxic Effects of Carvacrol and Thymol in Rat Bone Marrow Cells.” Environmental Toxicology, vol. 23, no. 6, Dec. 2008, pp. 728–735, 10.1002/tox.20380. Accessed 4 Jan. 2020.

48Deb, Dipanwita Dutta, et al. “Effect of Thymol on Peripheral Blood Mononuclear Cell PBMC and Acute Promyelotic Cancer Cell Line HL-60.” Chemico-Biological Interactions, vol. 193, no. 1, Aug. 2011, pp. 97–106,, 10.1016/j.cbi.2011.05.009. Accessed 4 Jan. 2020.

49Mohammadi-Samani, Soliman, et al. “Meloxicam Transdermal Delivery: Effect of Eutectic Point on the Rate and Extent of Skin Permeation.” Iranian Journal of Basic Medical Sciences, vol. 17, no. 2, 2014, pp. 112–8, Accessed 4 Jan. 2020.


51Ozkan, Aysun, and Ayse Erdogan. “A Comparative Study of the Antioxidant/Prooxidant Effects of Carvacrol and Thymol at Various Concentrations on Membrane and DNA of Parental and Drug Resistant H1299 Cells.” Natural Product Communications, vol. 7, no. 12, Dec. 2012, p. 1934578X1200701, 10.1177/1934578×1200701201. Accessed 4 Jan. 2020.

52Cizauskaite U, Bernatoniene J. Innovative Natural Ingredients-Based Multiple Emulsions: The Effect on Human Skin Moisture, Sebum Content, Pore Size and Pigmentation. Molecules. 2018;23(6)

53Boisvert, William A., et al. “Hair Growth-Promoting Effect of Geranium Sibiricum Extract in Human Dermal Papilla Cells and C57BL/6 Mice.” BMC Complementary and Alternative Medicine, vol. 17, no. 1, 13 Feb. 2017, 10.1186/s12906-017-1624-4. Accessed 4 Jan. 2020.

54Madrigal-Santillán, Eduardo. “Hepatoprotective Effect OfGeranium Schiedeanumagainst Ethanol Toxicity during Liver Regeneration.” World Journal of Gastroenterology, vol. 21, no. 25, 2015, p. 7718, 10.3748/wjg.v21.i25.7718. Accessed 22 Nov. 2019.

55Nadjib Boukhatem, Mohamed, et al. “Rose Geranium Essential Oil as a Source of New and Safe Anti-Inflammatory Drugs.” Libyan Journal of Medicine, vol. 8, no. 1, Jan. 2013, p. 22520, 10.3402/ljm.v8i0.22520. Accessed 4 Jan. 2020.

56Maruyama, Naho, et al. “Suppression of Neutrophil Accumulation in Mice by Cutaneous Application of Geranium Essential Oil.” Journal of Inflammation, vol. 2, no. 1, 2005, p. 1, 10.1186/1476-9255-2-1. Accessed 4 Jan. 2020.

57Sienkiewicz, Monika, et al. “The Biological Activities of Cinnamon, Geranium and Lavender Essential Oils.” Molecules, vol. 19, no. 12, 12 Dec. 2014, pp. 20929–20940, 10.3390/molecules191220929. Accessed 20 Oct. 2019.

58Bigos, Monika, et al. “Antimicrobial Activity of Geranium Oil against Clinical Strains of Staphylococcus Aureus.” Molecules (Basel, Switzerland), vol. 17, no. 9, 2012, pp. 10276–91,, 10.3390/molecules170910276. Accessed 21 June 2019.

59Gallardo, A., et al. “Insecticidal Activity of Individual and Mixed Monoterpenoids of Geranium Essential Oil Against Pediculus Humanus Capitis (Phthiraptera: Pediculidae).” Journal of Medical Entomology, vol. 49, no. 2, 1 Mar. 2012, pp. 332–335,, 10.1603/me11142. Accessed 4 Jan. 2020.

60Venskutonis, Petras Rimantas, et al. “A Preliminary Assessment of Singlet Oxygen Scavenging, Cytotoxic and Genotoxic Properties of Geranium Macrorrhizum Extracts.” Acta Biochimica Polonica, vol. 57, no. 2, 6 May 2010,, 10.18388/abp.2010_2389. Accessed 4 Jan. 2020.

61Miresmailli, Saber, and Murray B. Isman. “Efficacy and Persistence of Rosemary Oil as an Acaricide Against Twospotted Spider Mite (Acari: Tetranychidae) on Greenhouse Tomato.” Journal of Economic Entomology, vol. 99, no. 6, 1 Dec. 2006, pp. 2015–2023,, 10.1093/jee/99.6.2015. Accessed 4 Jan. 2020.

62Wikipedia Contributors. “Rosemary.” Wikipedia, Wikimedia Foundation, 7 Oct. 2019,

63Isman, Murray B., et al. “Insecticidal Activities of Commercial Rosemary Oils (Rosmarinus Officinalis.) Against Larvae OfPseudaletia Unipuncta. AndTrichoplusia Ni. in Relation to Their Chemical Compositions.” Pharmaceutical Biology, vol. 46, no. 1–2, Jan. 2008, pp. 82–87, 10.1080/13880200701734661. Accessed 4 Jan. 2020.

64Slameňová, Darina, et al. “Rosemary-Stimulated Reduction of DNA Strand Breaks and FPG-Sensitive Sites in Mammalian Cells Treated with H2O2 or Visible Light-Excited Methylene Blue.” Cancer Letters, vol. 177, no. 2, Mar. 2002, pp. 145–153,, 10.1016/s0304-3835(01)00784-4. Accessed 4 Jan. 2020.

65Yesil-Celiktas, Ozlem, et al. “Inhibitory Effects of Rosemary Extracts, Carnosic Acid and Rosmarinic Acid on the Growth of Various Human Cancer Cell Lines.” Plant Foods for Human Nutrition, vol. 65, no. 2, 7 May 2010, pp. 158–163, 10.1007/s11130-010-0166-4. Accessed 16 Mar. 2019.

66Moghtader, M. ; Afzali, D. “CAB Direct.” Cabdirect.Org, 2019, Accessed 4 Jan. 2020.

67Zorica Stojanović-Radić, et al. “Antimicrobial Activity and Cytotoxicity of Commercial Rosemary Essential Oil (Rosmarinus Officinalis L.).” Biologica Nyssana, vol. 1, no. 1–2, 2010, Accessed 4 Jan. 2020.

68Maistro, E.L., et al. “Genotoxicity and Mutagenicity of Rosmarinus Officinalis (Labiatae) Essential Oil in Mammalian Cells in Vivo.” Genetics and Molecular Research, vol. 9, no. 4, 2010, pp. 2120–2129,, 10.4238/vol9-4gmr857. Accessed 4 Jan. 2020.

69Europe PMC. “Europe PMC.” Europepmc.Org, 2016, Accessed 4 Jan. 2020.

70Martha, et al. “INTRA UTERINE GROWTH RETARDATION IN RATS TREATED WITH ESSENTIAL OIL OF ROSMARINUS OFFICINALIS LINN.” Revista Interdisciplinar de Estudos Experimentais – Animais e Humanos Interdisciplinary Journal of Experimental Studies, vol. 1, no. 1, 2010, Accessed 4 Jan. 2020.

71Wu, Huaxing, et al. “Inhibitory Effect and Possible Mechanism of Action of Patchouli Alcohol against Influenza A (H2N2) Virus.” Molecules, vol. 16, no. 8, 3 Aug. 2011, pp. 6489–6501,, 10.3390/molecules16086489. Accessed 4 Jan. 2020.

72Bacci, Leandro, et al. “Toxicity, Behavior Impairment, and Repellence of Essential Oils from Pepper-Rosmarin and Patchouli to Termites.” Entomologia Experimentalis et Applicata, vol. 156, no. 1, 27 May 2015, pp. 66–76, 10.1111/eea.12317. Accessed 4 Jan. 2020.

73Özcan, Musa. “Antifungal Properties of Propolis.” Grasas y Aceites, vol. 50, no. 5, 30 Oct. 1999, pp. 395–398, 10.3989/gya.1999.v50.i5.685. Accessed 14 May 2019.

74Mahmoud Lotfy. Biological Activity of Bee Propolis in Health and Disease. Accessed 4 Jan. 2020.

75Chauzat, Marie-Pierre, and Jean-Paul Faucon. “Pesticide Residues in Beeswax Samples Collected from Honey Bee Colonies (Apis Mellifera L.) in France.” Pest Management Science, vol. 63, no. 11, 2007, pp. 1100–1106, 10.1002/ps.1451. Accessed 20 Aug. 2019.

76Stefan Bogdanov. “Contaminants of Bee Products.” Apidologie, Apidologie 37 (2006) 1-18, 13 Dec. 2005, 01/M5401/M5401.html. Accessed 4 Jan. 2020.

77Frank M. Painter, D.C. “Natural vs. Synthetic Vitamin E.” Chiro.Org, 2013, Accessed 4 Jan. 2020.

78Enshaieh S, Jooya A, Siadat AH, Iraji F. The efficacy of 5% topical tea tree oil gel in mild to moderate acne vulgaris: a randomized, doubdffle-blind placebo-controlled study. Indian J Dermatol Venereol Leprol. 2007;73(1):22-5.

79David C. Liao, MD,. “Management of Acne.” Mdedege. Web. 23 Feb 2020. <>.

80Shah SGS. A Commentary on “Ensuring safe surgical care across resource settings via surgical outcomes data & quality improvement initiatives” (Int J Surg 2019 Aug 5. 10.1016/j.ijsu.2019.07.036). Int J Surg. 2019;72:14-15.

81Walton SF, Mckinnon M, Pizzutto S, Dougall A, Williams E, Currie BJ. Acaricidal activity of Melaleuca alternifolia (tea tree) oil: in vitro sensitivity of sarcoptes scabiei var hominis to terpinen-4-ol. Arch Dermatol. 2004;140(5):563-6.

82Zhang X, Guo Y, Guo L, Jiang H, Ji Q. Evaluation of Antioxidant and Antimicrobial Activities of Essential Oil. Biomed Res Int. 2018;2018:2396109.

83Zhang X, Guo Y, Guo L, Jiang H, Ji Q. Evaluation of Antioxidant and Antimicrobial Activities of Essential Oil. Biomed Res Int. 2018;2018:2396109.

84Southwell, I.A., Hayes, A.J., Markham, J. and Leach, D.N. (1993). THE SEARCH FOR OPTIMALLY BIOACTIVE AUSTRALIAN TEA TREE OIL. Acta Hortic. 344, 256-265. DOI: 10.17660/ActaHortic.1993.344.30.

85Shah SGS. A Commentary on “Ensuring safe surgical care across resource settings via surgical outcomes data & quality improvement initiatives” (Int J Surg 2019 Aug 5. 10.1016/j.ijsu.2019.07.036). Int J Surg. 2019;72:14-15.

86Shah SGS. A Commentary on “Ensuring safe surgical care across resource settings via surgical outcomes data & quality improvement initiatives” (Int J Surg 2019 Aug 5. 10.1016/j.ijsu.2019.07.036). Int J Surg. 2019;72:14-15.

87Shah SGS. A Commentary on “Ensuring safe surgical care across resource settings via surgical outcomes data & quality improvement initiatives” (Int J Surg 2019 Aug 5. 10.1016/j.ijsu.2019.07.036). Int J Surg. 2019;72:14-15.

88Shah SGS. A Commentary on “Ensuring safe surgical care across resource settings via surgical outcomes data & quality improvement initiatives” (Int J Surg 2019 Aug 5. 10.1016/j.ijsu.2019.07.036). Int J Surg. 2019;72:14-15.

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