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What causes dandruff? We asked Bill Nye the 'Science Guy' to break it down

Plus, he shares the ingredient that could be making it worse.
TODAY Illustration / Courtesy Bill Nye / AndreyPopov / Getty Images

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Dealing with an itchy, flakey scalp is no fun. But as annoying and embarrassing as dandruff may be, it's actually more common than you may think — it's estimated to affect around 50 percent of the adult population worldwide.

It's even something that beloved television personality and "Science Guy" Bill Nye has struggled with. "When I was in high school, I was very troubled by my scalp health," Nye told Shop TODAY during a Zoom interview. But now, when we joined him, along with Dr. Jeni Thomas, Global Science Communications Director for Procter & Gamble Hair, he was proudly sporting a black lab coat — which anyone with dandruff knows is a pretty big deal. "Check me out, I'm confident," he said. For the flake-free look, he credits Head & Shoulders, whose products he has used since those early days.

So we asked Nye, who is currently partnering with Head & Shoulders, to do what he does best and break down some of the science behind the condition, and the best ways to treat it.

What causes dandruff?

"There's a fungus among us," Nye said. The fungus in question is Malassezia globosa, which Nye said feeds off the oil on your skin (aka the sebum) and creates a waste product that irritates your scalp and causes you to shed skin cells faster. The fungus is everywhere, but it only affects about 50 percent of the population. "It's not a bacterium, and you are not an unhealthy person if you have this fungus, the fungus is everywhere," Nye said. "It's your genetics, it's your inheritance that makes you respond to it."

How to treat dandruff

To treat it, you want to look for a product with zinc pyrithione (ZPT) or selenium sulfide. "ZPT and selenium sulfide are rooted in minerals," Thomas said. "They are then turned into these active ingredients that have been clinically proven to fight dandruff."

"Fungus just doesn’t grow where these minerals are present," Nye said.

For most people, the obvious solution would be to grab a dandruff shampoo that includes the ingredients and call it a day. But according to Nye, using both a dandruff-fighting shampoo and conditioner is the better option. "When you don't use a conditioner, you wash half of [the zinc pyrithione] away," he said.

While there are plenty of dandruff remedies on the market, the experts said that these ingredients target the source of dandruff (the fungus). The trendy process of using a scalp brush for exfoliation, on the other hand, is more of a temporary fix. "That's going to be something that might temporarily remove the flakes that you have, but it's not getting to the source of dandruff, so you're only going to have those flakes come back," Thomas said.

And because dandruff is caused by this fungus, more so than a dry scalp, putting a hydrating oil on the area probably won't have the effect you're hoping for — in fact, it might just make it worse. "There are some sort of folk remedies that involve putting oil on your scalp or oil in a shampoo or something — oil leads to fungus ... that is an intuitive idea that absolutely does not work."

Thomas said the same can be said about using an essential oil, like tea tree oil to treat the issue. "Oils, in general, are adding to that problem of giving the fungus what it thrives off of," Thomas added. "And, I'd say even more so it's not getting to the root of the cause of dandruff. So even if it might feel good, and that idea of oils and there's so much love for them, they can be great for other purposes, but not for resolving dandruff."

With that in mind, we rounded up some popular treatment options that include those star dandruff-fighting ingredients.

Head & Shoulders Supreme Clarify & Volumize Shampoo and Conditioner

This item is from a brand that Nye is paid to promote.

According to Nye, the size of the zinc pyrithione molecules is what makes Head & Shoulders formulas so effective, stating "the molecules that they've [Head & Shoulders has] got in suspension carried with the shampoo are smaller." As a result, he said, they spread out better in the funnel from which the hair follicle hair grows.

More top-rated dandruff shampoos

First Aid Beauty Anti-Dandruff Shampoo

Made with 1 percent ZPT, this shampoo from First Aid Beauty is designed to soothe scalp irritation and combat dandruff to leave your hair looking smooth and flake-free. For best results, the brand says that it should be used twice per week.

Dove DermaCare Scalp Anti-Dandruff Conditioner

Not only does this conditioner promise to help fight flakes (thanks to the inclusion of ZPT), but it's also made with moisturizing ingredients, which the brand says improves scalp redness and dryness.

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