Selenium shampoos (Selsun Blue®, Exsel®, Head and Shoulders Intensive Treatment Dandruff Shampoo®, selenium sulfide 1%) have been available since the 1950s. Their mechanism of action is unclear but it is believed they may be antimicrobial. They are used to treat dandruff, itching and flaking of the scalp, and tinea versicolor, a fungal infection of the skin.
Side effects can include oiliness or dryness of hair and scalp, hair loss and hair discoloration. Serious side effects include scalp irritation and skin irritation. If you experience these symptoms contact your physician.