Salicylic acid, also known as 2-lydroxybenzoic acid, C₆H₄(OH)COOH, is a colorless, crystalline solid, derivatives of which are used as analgesics (including aspirin, acetylsalicylic acid), antiseptics, dyes, and liniments. Salicylic acid is a keratolytic drug which causes the skin to peel and destroys bacteria and fungi. It is applied to the skin, alone or in combination with other agents, to treat warts (including verrucas), corns, calluses, acne, dandruff, psoriasis, and fungal infections. Skin sensitivity reactions may occur after continued use. Salicylic acid occurs naturally in plants, including willow bark. Molecular weight 138.1, melting point 159°. Methyl salicylate, an ester, occurs in oil of wintergreen, and is used as a liniment and as a flavoring.