Selenium sulfide is a topical antifungal agent used primarily to treat scalp conditions caused by fungus or yeast, such as seborrheic dermatitis (dandruff), tinea capitis (scalp ringworm), and tinea versicolor (discolored skin patches). It reduces flaking, itching, and irritation, and is available in 1% (over-the-counter) or 2.5% (prescription) strengths.