This study from 1990 found that...
The results of this study showed that both 5% tea-tree oil and 5% benzoyl peroxide had a significant effect in ameliorating the patients' acne by reducing the number of inflamed and non-inflamed lesions (open and closed comedones), although the onset of action in the case of tea-tree oil was slower. Encouragingly, fewer side effects were experienced by patients treated with tea-tree oil.
How does tea tree work? The researchers from this study in 2001 concluded...
These effects, along with the findings presented here, indicate that tea tree oil damages cell membrane structure in E. coli, Staph. aureus and C. albicans. The cytoplasmic membranes of bacteria and the plasma and mitochondrial membranes of yeast provide a barrier to the passage of small ions such as H+, K+, Na+ and Ca2+ and allow cells and organelles to control the entry and exit of different compounds. This permeability barrier role of cell membranes is integral to many cellular functions, including the maintenance of the energy status of the cell, other membrane-coupled energy-transducing processes, solute transport, regulation of metabolism and control of turgor pressure.
In other words, it makes the membranes of these little critters fail and they die. (Here's another paper detailing how they die, if you're into that sort of thing!)
study from 2008 notes...
[T]he tea-tree oils, terpinen-4-ol, oc-terpineol and α-pinene were found to be active against Staphylococcus aureus, Staph. epidermidis and Propionibacterium acnes whereas cineole was inactive against these organisms....This study supports the use of tea-tree oil in the treatment of acne, and demonstrates that terpinen-4-ol is not the sole active constituent of the oil.
And this study from 1998 notes that, "These data indicate that some essential oils are active against Candida spp., suggesting that they may be useful in the topical treatment of superficial candida infections." And this review notes that, "Data now show that a range of yeasts, dermatophytes, and other filamentous fungi are susceptible to TTO".
Tea tree oil is good against bacteria and yeasts: What about viruses? This review notes that, "The results of these studies indicate that TTO may act against enveloped and nonenveloped viruses, although the range of viruses tested to date is very limited." So the jury's still kind of out on the whole virus thing...
It's looking very promising indeed! It looks like we can use tea tree oil in products intended for those of us with acne and fungal infections! It's been suggested that 1% tea tree oil in a product is adequate, although some products can go up to 2%. This review noted that tea tree oil at lower levels might be bacteriostatic, rather than bactericidal.
What's the difference between bacteriostatic and bactericidal? Bactericidals will kill bacteria - note the "cidal" in there, like homicidal or suicidal - and bacteriostatics will limit the growth of the bacteria. It's still there, but if it can't grow, pretty soon they'll all be dead!
But it doesn't look like it works well as a hand cleanser! "A recent handwash study using volunteers showed that either a product containing 5% TTO and 10% alcohol or a solution of 5% TTO in water performed significantly better than soft soap, whereas a handwash product containing 5% TTO did not (review)."
But it does seem we can use it as an ingredient in a dandruff shampoo! (Although, disclaimer, I can only find one study from 2003 that found these results, the same study quoted by the review!)
The evaluation of a 5% TTO shampoo for mild to moderate dandruff demonstrated statistically significant improvements in the investigator-assessed whole scalp lesion score, total area of involvement score, and total severity score, as well as in the patient-assessed itchiness and greasiness scores, compared to placebo. Overall, the 5% TTO was well tolerated and appeared to be effective in the treatment of mild to moderate dandruff (review).
Is tea tree oil anti-fungal, anti-bacterial, anti-viral, anti-septic, wound healing, anti-inflammatory, and analgesic? I think we can safely say that the science leans towards it being an anti-fungal and anti-bacterial, but I don't think there's evidence that it is anti-viral. If we define anti-septic as a "microbial substance applied to living tissue or skin to reduce the possibility of infection, sepsis, or putrefaction", then I think we can say that is an anti-septic essential oil. This review noted there were many studies supporting the idea of it being an anti-inflammatory ingredient (click for specific section). As for being an analgesic, I guess we could define it that way - as being a thing that reduces pain - although I can't provide you with any studies on that front.
Wow! It really does live up to the hype!!!
Finally, can it act as a preservative for our products? Right now, my opinion is no, and I think the science backs me up on this. In this study, a combination of tea tree, lavender, and lemon essential oils were used with a synthetic preservative, and the researchers were able to reduce the preservative by 8.5 times (they used 0.1% preservative with 0.5% each of lavender and tea tree oil and get good preservation over time). But considering every product you make would smell of lavender and tea tree - not a winning combination, in my humble opinion - and given we don't have labs to get that combination just right, it doesn't sound like it's going to work for homecrafters any time soon!
Join me tomorrow as we take a look at some products in which we could include tea tree oil!