Tea tree oil is the most commonly-recommended oil when it comes to repelling something living; whether that’s bacteria or mold or fungus, tea tree is a go-to active ingredient in many natural products used for cleaning or disinfecting. Specifically, it is widely thought that tea tree oil can be useful in everything from clearing up acne and dandruff to disinfecting cuts to curing cancer. In this article, I’ll explore the claims made about tea tree oil and compare them to the research, helping you to know what the REAL benefits of tea tree oil are.
As a young scientist, I know how hard sifting through and understanding academic articles can be, so I endeavor to remove (or explain) the jargon for you guys, making this research accessible to everyone. Because this information shouldn’t be limited to people who know words like antiplasmid and ambulatory (or those who have a crazy amount of free time to google each word).
If you’re looking for very specific information about the background, regulations, composition, and safety for tea tree oil, check out this review paper.
Tea tree oil is mainly composed of terpene hydrocarbons, mainly monoterpenes, sesquiterpenes, and their associated alcohols. Terpenes are volatile, aromatic hydrocarbons and may be considered polymers of isoprene, which has the formula C5H8.
Even if the chemistry is over your head, the takeaways are one, that this oil will have a strong effect when concentrated and must never be used undiluted and two, that this oil is not safe to use around cats.
Let’s explore the claims made about tea tree oil:
- Toenail fungus/ringworm
I’ll start with an overview of the antimicrobial activity of the oil, which is likely responsible for the majority of claims on this list, and move on to a claim by claim evaluation of the oil.
Tea tree oil has been tested against a wide variety of bacteria and fungi, along with a few viruses and protozoa. Dissimilar to many drugs used to treat these infections, there have been no clinical reports of tea tree oil resistance developing.
Below, the effectiveness of tea tree oil on many microbes is listed. When looking at this data, it is important to remember that these are tests done in lab environments, and the clinical efficacy of tea tree oil can be more difficult to determine. This is due to a variety of factors, but a major factor is that when the oil is applied to the affected area, it is interacting with far more than just the pathogen; it comes in contact with your skin oils, other bacteria on your skin, your skin cells, etc. The concentrations listed are minimum for killing 99.9% in a lab environment, and you may need to use higher concentrations in practice. However, use caution, as it is dangerous to use high concentrations of essential oils regularly.
Tea tree oil (M. alternifolia) has been tested against several strains of bacteria. Although as discussed in my post about essential oils for cleaning, it is not the most potent oil you can use to kill the bacteria commonly found in areas like your bathroom and kitchen.
Here’s a list of the bacteria tea tree oil will work against, along with the MBC (minimum bactericidal concentration):
Acinetobacter baumannii – commonly found in hospitals, 1%
Actinomyces viscosus – colonizes the mouth of humans, 0.6%
Actinomyces spp. – general; usually infect wounds, 1%
Bacillus cereus – foodborne illness, known for being found in fried rice, 0.3%
Bacteroides spp. – gastrointestinal illness, 0.5%
Corynebacterium sp. – diptheria, 2%
Enterococcus faecalis – found in root canals and hospitals, 8%
E. faecium (vancomycin resistant) – neonatal meningitis and endocarditis, 1%
Escherichia coli – foodborne illness, 4%
Fusobacterium nucleatum – periodontal disease, 0.6%
Klebsiella pneumoniae – lung infection, 0.3%
Lactobacillus spp. – cavities, 2%
Micrococcus luteus – upper respiratory infections, 6%
Peptostreptococcus anaerobius – pelvic inflammatory disease, vaginal bacteriosis, 0.6%
Porphyromonas endodontalis – oral infections, 0.1%
P. gingivalis – periodontal disease, 0.6%
Prevotella spp. – respiratory infections, 0.25%
Propionibacterium acnes – linked to acne, 0.63%
Proteus vulgaris – wound infections, urinary tract infections, 4%
Pseudomonas aeruginosa – very drug resistant infection usually contracted in hospitals, 8%
Staphylococcus aureus – the commonly known staph infections, 2%
Staphylococcus epidermidis – common in hospitals, 4%
Staphylococcus hominis – contributes to body odor – 4%
Streptococcus pyogenes – commonly known ‘strep throat,’ 4%
It is important to note that many of the bacteria on this list represent an entire genus (group of similar bacteria), where some strains are harmful while others live in mutualistic symbiosis with the human body. I have listed the effects of the harmful strains for your reference, but some strains are used in probiotics and are perfectly fine in your body, so don’t be alarmed if you see some of these on food labels.
For those of you who are interested, the mechanism by which tea tree oil kills bacteria is accepted to be based on its hydrocarbon structure. Hydrocarbons can insert themselves into membranes and begin disrupting vital cell functions and membrane integrity. Once a bacteria loses its membrane integrity, the inside spills out and it dies.
Tea tree oil (M. alternifolia) has also been tested against several fungi. Here’s the list and the MFC (minimum fungicidal concentration:
Alternaria – hay fever, 2%
Aspergillus flavus – aspergilliosis, sometimes liver cancer, 4%
Aspergillus fumigatus – common invasive fungal infection in immunocompromised people, 2%
Aspergillus niger – black mold, 8%
Blastoschizomyces capitatus – rare cause of yeast infections, 0.25%
Candida albicans – common cause of yeast infections (oral and vaginal), 8%
Candida glabrata – can infect the urogential tract of immunocompromised people, 8%
Candida parapsilosis – can cause sepsis in wounds, 0.5%
Candida tropicalis – may contribute to Crohn’s disease, 2%
Cladosporium – one of the most common indoor/outdoor molds, 4%
Cryptococcus neoformans – common infection in the lungs of immunocompromised people, 0.06%
Epidermophyton floccosum – common gym/shower fungus, 0.7%
Fusarium – tends to infect barley crops, can cause head blight, 2%
Malassezia furfur – normally lives on the skin, but overgrowth can cause skin discoloration, 1%
Malassezia sympodialis – considered part of a healthy skin biome, but can cause eczema in susceptible individuals, 0.12%
Microsporum canis – can cause lesions on domesticated cats, dogs, sometimes humans, 0.5%
Microsporum gypseum – infects the upper layer of dead skin in mammals, 0.5%
Penicillium – some species produce penicillin, while others are plant pathogens, 2%
Rhodotorula rubra – can cause bloodstream infections in immunocompromised people, 0.5%
Saccharomyces cerevisiae – most commonly used for fermentation, but may be associated with Crohn’s disease, 0.5%
Trichophyton mentagrophytes – athlete’s foot, 0.5%
Trichophyton rubrum – athlete’s foot, jock itch, ringworm, 1%
Trichophyton tonsurans – ringworm of the scalp, 0.5%
Trichosporon – white piedra (encompasses hair follicles), 0.12%
Similarly to bacteria, tea tree oil kills most fungi by compromising their membrane integrity, making them susceptible to lysis (breaking open).
Tea tree oil has been tested against some viruses, but the research here is fairly limited. According to this review, tea tree oil shows activity against HSV-1 and HSV-2, and tobacco mosaic virus. However, the oil is only really effective on free viruses, meaning if it’s already inside a cell tea tree oil won’t be as helpful. The good news is that further testing is in progress, and it is believed that tea tree oil is effective against both enveloped and nonenveloped viruses.
Protozoa, apart from being the first rockstar in space (movie: Zenon, Girl of the 21rst Century), are unicellular eukaryotic organisms.
Tea tree oil has been studied against limited protozoa, but it has been shown effective against Leishmania major (Oriental sore), Trichomonas vaginalis (vaginitis, and STD) and Trypansosome brucci (African sleeping sickness).
Revisiting the claims made about tea tree oil
As mentioned in the antibacterial section, tea tree oil is effective against Propionibacterium acnes at a minimum concentration of 0.63%. While this bacteria is not the only cause of acne, it is very often involved in the presence of acne, and is a target for many acne-reducing products.
According to this review of tea-tree oil acne products, tea tree oil is often used as a 5% gel, and is widely reported as “effective at reducing lesions on the skin.” However, there is a distinct lack of statistical analysis in these studies, even though many of them are double-blind (this reduces investigator and patient bias). From this information I can say that trying tea tree oil as an acne solution is a valid treatment, but I cannot say to what extent. I also cannot say it will work for everyone, as the exact cause of each person’s acne is a little bit different.
Bottom line: Might be effective, go ahead and try it.
For quite awhile, we have known that lice have been developing drug resistance, and researchers are beginning to study essential oils as alternative treatments.
Clinical studies are not yet widespread, but in vitro (lab-based) studies have shown that tea tree oil is effective at killing adult lice (1% concentration after 30 mins), and eggs (4% concentration killed 100% of eggs after 10 days). In this particular study, the lice were collected from the heads of children in Italy; this is important because often the resistance of lice is dependent on the area it lives in.
More research should be done to determine the long-term effectiveness of tea tree oil against lice in many countries, but research to date is promising.
Bottom line: Most likely effective
There seems to be limited studies on this claim. There is a prominent study, single blind, that finds that 5% tea tree oil shampoo has statistically significant effects on dandruff severity. However, this is pretty much the only reliable study to directly test tea tree oil against dandruff in a clinical setting.
In lab environments, tea tree oil is effective against the fungus thought to be associated with dandruff, Pityrosporum ovale (sometimes known as Malassezia furfur), at a minimum concentration of 0.25%.
Bottom line: Evidence is slim, but this remedy is safe to try.
Going back to the antifungal section, we see that tea tree oil is effective against Malassezia sympodialis, which, while part of a healthy skin biome, can cause eczema in susceptible individuals. Researchers still aren’t quite sure what makes someone susceptible to developing eczema, but many believe it is passed along genetically.
There is one major study, done on dogs, that suggests that a 10% tea tree oil cream has a statistically significant effect on reducing eczema. The cream was applied daily for 4 weeks, and 82% of dogs showed a good response to the treatment.
In general, there is not a lot of evidence to support tea tree oil as a treatment for eczema. Trustworthy clinical trials on humans do not exist to date, and our understanding of the causes of eczema is too limited to truly delve into the specifics of treating it.
Bottom line: Very slim evidence, but this remedy is safe to try.
Toenail fungus and ringworm
Looking back to the antifungal section, we can see that tea tree oil is effective against fungi that are known to cause both athlete’s foot and ringworm, at a concentration of 1%. However, this is only an in vitro report.
When we look at clinical studies on actual humans, the concentrations used goes way up. This study tests both 25% and 50% tea tree oil solutions on feet, and evaluates the effectiveness after daily application for 4 weeks. After 4 weeks, 64% of the tea tree oil patients were considered ‘cured’ mycologically, compared to 13% of the placebo group. The reason for the high concentrations used may be due to an earlier study, conducted in 1992, which found that 10% tea tree oil did not perform statistically better than placebo. The researchers in this study also gloss over the fact that 4 of their patients developed dermatitis from the high concentrations of tea tree oil.
Bottom line: There is evidence of effectiveness at high concentrations, but at these concentrations risk of developing dermatitis is non-negligable. I don’t consider this a safe remedy to try.
Many websites claim the effectiveness of tea tree oil against household mold, but many don’t specify the type. A few do specifically claim black mold, though, and there is evidence for this. According to antifungal data summarized above, tea tree oil is effective against Aspergillus niger – black mold, at a minimum fungicidal concentration of 8%.
Since treating black mold in your home has nothing to do with a disease inside a living being, laboratory testing on this fungus is pretty reliable. You are also free to use higher concentrations of tea tree oil when treating this mold because you’re not applying it to yourself. The only concern here might be the possible effect it has on the surface you apply it to, such as discoloration or a slight breakdown, depending on the material.
Bottom line: This should work. Use an 8% or higher solution, but test on a small area to avoid damaging materials in your home.
This claim also relies on the antibacterial properties of tea tree oil. Looking back at our list, we can see that tea tree oil is effective against Staphylococcus hominis at a concentration of 4%. This bacteria is known to contribute to body odor, although it is not the sole cause.
However, there are no studies suggesting that tea tree oil is effective at reducing body odor. But then again, we don’t have any suggesting it is ineffective either.
Bottom line: We really don’t know, but this remedy is safe to try.
Cancer – Melanoma
In every case, this claim is always hard to prove or disprove, because so many factors contribute to cancer development and therefore its susceptibility to certain treatments. And while I can talk to you about some of the research being done here, I cannot ever confidently suggest that you use tea tree, or any other essential oil, as your only means of fighting cancer.
There is some evidence that topical application of tea tree oil can inhibit the growth of melanoma, and even interfere with otherwise drug-resistant varieties. While the results seem promising, as far as I can tell there are only two studies looking at this, both of them dated 2011 and earlier. Otherwise, there is one study in rats testing tea tree oil against tumors in the skin, and while it was found to be cytotoxic to tumor cells, it was found to be ineffective at clearing the tumor.
Bottom line: Don’t rely on tea tree oil as a cancer treatment.
There are now numerous studies that support the anti-inflammatory effect of tea tree oil both in vitro (in a lab) and in vivo (in a living thing) (studies summarized here).
In summary, tea tree oil is known to reduce normal inflammatory responses. These are the responses that happen when injury occurs, such as a cut or a bruise. Tea tree oil will reduce swelling and thus may help relieve pain due to swelling.
Tea tree oil is also studied in the histamine reaction. This is usually known as an allergic reaction (thus why we take anti-histamines for allergies). Tea tree oil will not prevent allergic reactions, but they will help reduce irritation due to one.
Bottom line: Tea tree oil is effective against normal inflammation.
So to recap, the verified uses for tea tree oil are:
- Lice treatment
- Black mold
What are your experiences with tea tree oil? What are your favorite ways to use it? Let me know! Let’s chat in the comments below.
If you loved this article, you can read more Just the Facts posts here.
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