Selenium sulfide is a chemical compound commonly used in medicinal shampoos and lotions to treat skin conditions like dandruff and seborrheic dermatitis. It works by reducing the growth of fungi and yeast on the skin, helping to alleviate itching and flaking. In addition to its antifungal properties, selenium sulfide can also help to slow down the production of skin cells, which is beneficial for conditions where skin cells multiply too quickly. It is typically available in over-the-counter products and should be used as directed for effective results.