Selsun Dandruff Shampoo Blue reduces itching, flaking, irritation, and redness of the scalp. Selenium sulfide is also used for a condition that causes discoloration of the skin (tinea versicolor). Tough on dandruff, great for hair . Targets the source to control dandruff . Directions to Use : Massage into wet hair, lather and rinse thoroughly. For better results use twice a week.