Dandruff can last for a long time, depending on the severity of the condition. If dandruff is caused by dry skin, it can often be resolved by simply increasing the moisture in the scalp. This can be done by using a mild shampoo and conditioner, and by avoiding harsh chemicals and hot showers. If dandruff is caused by an overgrowth of yeast on the scalp, it can be treated with medicated shampoos containing selenium sulfide or zinc pyrithione.