What causes dandruff, and how do you get rid of it? - Thomas L. Dawson

Here in this abundant forest, Malassezia is equipped with everything it could ever need. Feasting constantly, it’s in paradise. But wait—what’s this? In fact, Malassezia is a type of yeast that lives and dines on all of our scalps. And in about half of the human population, its activity causes dandruff.

So, why do some people have more dandruff than others? And how can it be treated? We might consider ourselves individuals, but we’re really colonies. Our skin hosts billions of microbes. Malassezia yeasts make themselves at home on our skin shortly after we’re born. Follicles, the tiny cavities that grow hairs all over our body, make for especially popular living quarters.

Malassezia are fond of these hideouts because they contain glands that secrete an oil called sebum that’s thought to lubricate and strengthen our hair. Malassezia evolved to consume our skin’s proteins and oils. And because of its many sebum-secreting follicles, our scalp is one of the oiliest places on our body—and consequently, one of the yeastiest.

As these fungi feast on our scalp’s oils, dandruff may form. This is because sebum is composed of both saturated and unsaturated fatty acids. Saturated fats neatly pack together. Unsaturated fats, on the other hand, contain double bonds that create an irregular kink in their structure.

Malassezia eat sebum by secreting an enzyme that releases all of the oil’s fatty acids. But they only consume the saturated fats, leaving the unsaturated ones behind. These irregularly shaped leftovers soak into the skin and pry its barrier open, allowing water to escape. The body detects these breaches and responds defensively, causing the inflammation that gives dandruff its itch.

It also makes the skin cells proliferate to repair the damaged barrier. Usually, our skin’s outer surface, or epidermis, completely renews itself every two to three weeks. Epidermal cells divide, move outwards, die, and form the skin’s tough outer layer, which gradually sheds off in single cells far too small to see.

But with dandruff, cells churn out quickly to correct the broken barrier, meaning they don’t mature and differentiate properly. Instead, they form large, greasy clumps around the hair follicle that are shed as visible flakes. This is how Malassezia’s voracious appetite and our body's reaction to its by-products lead to dandruff.

Currently, the most effective way to get rid of dandruff is by using antifungals in things like shampoos, applied directly to the scalp, to kill Malassezia. For those who experience dandruff, it usually comes and goes as sebum secretions vary throughout one's lifetime due to hormonal changes.

But despite the fact that Malassezia colonize everyone to a similar extent, not everyone gets dandruff. Some people are more susceptible. Exactly why is unclear. Do people with dandruff have a certain genetic predisposition? Is their skin barrier more permeable?

Scientists are currently investigating if people with dandruff do, in fact, lose more water through their scalps, and whether this is what’s leading their skin cells to proliferate. Researchers are learning that Malassezia communicate with our immune system using small, oily molecules called oxylipins that regulate inflammation.

If they can find a way to inhibit inflammatory oxylipins and boost anti-inflammatory ones, they could develop new treatments. Scientists are also investigating if there’s any benefit to our relationship with Malassezia. They hypothesize that dandruff, which can be uncomfortable and embarrassing for us, creates a reliable, oily food source for the yeast.

But dandruff isn’t contagious or a great threat to our health. And Malassezia seem to excel at defending their territory, our skin, from other, more harmful microbes like Staphylococcus aureus. So, while scientists have gotten to the bottom of many mysteries surrounding this condition, it must be said: dandruff remains a head-scratcher.