“It can stick with you throughout your adult years,” Dr. Thomas says. “It can come in phases.”

Whenever it may occur, the solution is to use a dandruff shampoo containing zinc pyrithione. But Nye urges you to follow it up not with a regular conditioner, but one specifically meant for dandruff. “So if you use anti-dandruff shampoo — OK, that’s good. This fungus does not enjoy eating your skin oil combined with zinc. Doesn’t dig it,” Nye says. “But then, when you condition without the zinc, you’re washing away about half of the zinc pyrithione, so you’re undoing what you just did. But with conditioners that have that active ingredient in it, you’re not undoing it — you’re doing it.”  

And this goes for people with a dry scalp, too. Yes, the greasy flakes of dandruff and dusty flakes of a dry scalp are not the same thing, but they are related. “Dry scalp flakes and dandruff flakes are rooted in the same issue,” Dr. Thomas says. “So to Bill’s point, I would say, give an anti-dandruff shampoo a try and see if that addresses your dry scalp problem.”

What Nye would urge you to not do if you have a dry scalp (or any kind of scalp, for that matter) is to use oil to try to moisturize it. “There may be a perception that if your skin feels dry, you put oil on it,” he says. “Well, if you add oil to your scalp, you’re just providing more fuel for this fungus. So I recommend against that.”

Heidi Prather, MD, a board-certified dermatologist based in Texas, agrees with the recommendation. “Over-treating the scalp with oil-based hair products may exacerbate dandruff,” she previously told Allure.

Nye doesn’t struggle with dandruff the way he did as teen, which may have something to do with getting older — Dr. Thomas says oil production isn’t quite as robust after age 60 — or it may have something to do with his fondness for Head & Shoulders’ Clinical Strength line, which, in addition to zinc pyrithione, contains another dandruff-suppressing mineral called selenium disulfide.

Ultimately, no matter which dandruff formula you choose, it’s important to stick to it, even when things are looking less flaky. Dr. Thomas calls it maintenance mode. Nye sees it more like staying ahead of the “competition” — the fungus.