 Our entire understanding of the cause of dandruff shifted with this landmark article published in 1984. Instead of relying on secondary sources, reviews, editorial opinion pieces, he looked at the primary literature, the original studies, and was amazed to find out how overwhelming was the evidence of the true cause and how it had been ignored because it was so well buried under the mountain of error since some expert in the 1800s put forth some bogus theory. We now know that dandruff is triggered by a fungus that lives and feeds on the human scalp. The two major implications being, first, how alarming it is that some bogus theory can remain in the medical literature unchallenged for a century, despite evidence to the contrary. And second, hey, if it's a fungus, what about trying tea tree oil, which contains components that have anti-fungal activity against a range of fungi? That was based on studies like this, though, where tea tree oil in a tea tree dish can fight off pathogenic skin fungi, but you don't know if it works for dandruff until you put it to the test. 126 men and women randomized the daily use of a 5% tea tree oil shampoo or placebo for a month. The placebo worked a little bit, decreasing dandruff severity by about 10%, but the tea tree oil shampoo worked better, about a 40% drop. It looks like more than 40% from the graph, but that's because they misleadingly started the Y-axis at negative 60%. This is a classic deception featured in chapter 5 of the 1954 classic How to Lie with Statistics. The graph should really look like this, which makes the effect less impressive, but it was still statistically significant. Only one patient in the tea tree oil group have actually achieved a complete response, the one in the placebo group did as well. Thus it seems that the tea tree oil shampoo would require ongoing application for control of dandruff. Speaking of fungus, what about tea tree oil in the treatment of athlete's foot? That may actually be our most common fungal skin infection, affecting up to 1 in 10. So about 100 patients randomized into one or three groups. A 10% tea tree oil cream, tinnactin, an antifungal drug, or a placebo cream. A month later, the fungus was wiped out in 85% of the drug group, but only about a quarter of the placebo in tea tree oil groups. This is somewhat surprising, since tea tree oil can kill off the fungus in a petri dish, but apparently not on toes. That reminds me of some of the oral health data on tea tree oil. I mean, I can wipe out some oral pathogens in a petri dish, but have people swish a tea tree oil solution around their mouth? And here's the dental plaque buildup after four days of no brushing, swishing with a placebo. Here's swishing with a medicated chlorhexidine mouthwash, which helps keep the plaque a bit at bay, but the tea tree oil mouth rinse? No effect. So if tea tree oil doesn't influence the amount of plaque, presumably it wouldn't help with gingivitis, the gum inflammation that's caused by plaque buildup. But no, here's the twist. True, no reduction in plaque with a 2.5% tea tree oil gel, yet significant reduction in gingivitis scores. Since decreased gum inflammation occurred without a decrease in plaque, it appeared to just be helping more from an anti-inflammatory, rather than an antimicrobial mechanism. Might the same thing be happening here? Yeah, from a mycological cure standpoint, a fungus cure standpoint, tea tree oil didn't really do any better than placebo. But though the drug wiped out the fungus in 85% of cases, in some of those cases, the patient actually didn't notice an improvement in symptoms, or they actually felt worse after the drug, probably a reflection of tinnactin's irritant side effects. If instead of mycological cure, you looked at symptom improvement, tea tree oil works as well as the drug. So this may be the basis for the popular use of tea tree oil in the treatment of athlete's foot. But people should realize it's just symptomatic relief, and they're not necessarily eliminating the underlying clause. Of course, maybe they didn't use a strong enough concentration. And indeed, if you go with not a 10% cream, but up to 25% or 50%, you can get mycological cure rates above that of placebo, but still not as good as the drug. And in those high concentrations, some of the patients applying tea tree oil developed moderate to severe dermatitis. They broke out in a rash. But hey, if you have a patient that doesn't want to use the medicated creams, then a 25% tea tree oil application is a decent chance of knocking it out without being too risky. But the standard over-the-counter antifungal creams may work better.