This medication is used to treat a variety of fungal skin infections such as ringworm, athlete’s foot, and jock itch. This medication is also used to treat a skin condition known as pityriasis (tinea versicolor), a fungal infection that causes a lightening or darkening of the skin of the neck, chest, arms, or legs. Terbinafine is an antifungal that works by preventing the growth of fungus.