astringent (əstrĭnˈjənt) [key], substance that shrinks body tissues. Astringent medicines cause shrinkage of mucous membranes or exposed tissues and are often used internally to check discharge of serum or mucous secretions in sore throat, hemorrhage, diarrhea, or peptic ulcer. Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin. Mildly astringent solutions are used in the relief of such minor skin irritations as those resulting from superficial cuts, allergies, insect bites, or athlete's foot. Astringent preparations include silver nitrate, zinc oxide, calamine lotion, tincture of benzoin, and vegetable substances such as tannic and gallic acids, catechu, and oak bark. Some metal salts and acids have also been used as astringents.