disulfide for which evidence is much more limited. However, the review did suggest use of over-the-counter selenium disulfide shampoos as an inexpensive option for managing mild symptoms of seborrheic dermatitis. Available forms Selenium disulfide is available in the form of a prescription drug as a 2.5% medical shampoo. In the United States, a 1% strength is available over-the-counter, and a 2.5% strength is also available with a prescription. In Canada, the 2.5% strength is available over-the-counter. Selsun Blue is an over-the-counter shampoo for dandruff with 1% selenium disulfide as its active ingredient. Side effects Side effects of selenium disulfide shampoo for dandruff appear to be infrequent. A randomized controlled trial of 100 people who received selenium disulfide reported side effects of itching or burning sensation of the scalp (3people), eruption near the hairline (1person), psoriasis (1person), lightening or bleaching of hair color (2people), orange staining of the scalp (1person), and a chemical taste while shampooing (1person). Selenium disulfide can cause discoloration of nails and light hair and can alter the color of hair dyes. Several scattered case reports of orange to red–brown scalp discoloration with selenium sulfide shampoo exist. The discoloration resolved shortly following discontinuation of selenium disulfide shampoo and its removal could be facilitated by lightly swabbing with isopropyl alcohol. Selenium disulfide may also discolor metallic jewellery. Case reports of temporary diffuse hair loss with selenium disulfide shampoo exist as well. Excessive environmental or occupational exposure to selenium has also been associated with hair loss and other adverse effects. However, hair loss has not been reported with topical selenium disulfide in several large studies. Selenium disulfide should not be applied to damaged skin as there is a risk of systemic absorption and associated toxicity. Systemic symptoms may include tremors, weakness, lethargy, lower abdominal pain, and occasional vomiting. These symptoms usually resolve within 10days following exposure. Pharmacology Pharmacodynamics Selenium disulfide acts as an antifungal and keratolytic agent to treat seborrheic dermatitis and dandruff. Pharmacokinetics The systemic absorption and toxicity of orally administered selenium sulfide has been studied in animals. Topical use of selenium sulfide in the form of a shampoo or lotion in humans does not appear to normally increase circulating or urinary selenium levels. However, application of selenium disulfide to damaged skin can result in systemic absorption and has been associated with cases of toxicity. Selenium disulfide appears to be much less toxic than other selenium salts, which may