Dandruff refers to the fine, white flakes that come off your scalp, though other symptoms include scalp itching, tightness, and even redness. The cause? A particular type of fungus that lives on the scalp (gross, but true) known as Malassezia ovalis. Some people are especially sensitive to this yeast, and that reaction can cause both inflammation and an excessive growth of skin cells. Those extra skin cells then stick together and fall off as, you guessed it, flakes. And the inevitable itchiness that can come with it doesn’t help matters, since scratching only causes more inflammation and makes matters worse.