Reduce itching and flaking and prevent further build up of dandruff with Selsun Suspension Anti-Dandruff Shampoo. It contains selenium sulfide, which belongs to a class of drugs called antifungals. It works by slowing down the growth of yeast that causes infections such as dandruff. It prevents dandruff by reducing the oiliness of the scalp and slowing the growth of the layer of skin cells on the scalp that causes dandruff.