Most people think dandruff is caused by dry skin, but that’s really not the case. Here’s the real deal: All humans have a harmless little fungus living on our scalps. It hangs out up there feeding on our dead skin cells and oils. Sometimes, this organism can cause our scalps to shed skin cells too quickly. These cells are really sticky and form big globs of scale that are visible as dandruff, explains Dr. Hilary Baldwin, a dermatologist in Brooklyn, New York. As you may realize, these small, white flakes won’t hurt you at all. Sometimes, though, your head may be itchy, especially in the winter when your skin is naturally dryer anyway. More importantly, though, dandruff can be embarrassing-especially when you’re wearing a black shirt! Luckily, it’s easy to control this problem with over-the-counter shampoos. (They keep that little fungus at bay, which means your scalp is less irritated, flaky and dry.) Look for shampoos that contain anti-dandruff ingredients like salicylic acid, zinc pyrithione, sulfur, selenium, or ketoconazole. After lathering up for a week, you should have flake-free head and shoulders.