Astringent

An astringent is a substance that causes contraction or shrinkage of body tissues, typically through the action of tannins and related compounds that bind and precipitate proteins. Applied to skin or mucous membranes, an astringent produces mild protein coagulation, drying and protecting the surface, which is why astringents are used to treat acne, minor cuts, insect bites, hemorrhoids, and fungal infections such as athlete's foot. Taken internally, astringents constrict mucous membranes to reduce discharge in conditions such as sore throats, diarrhea, and peptic ulcers. Common astringent agents include alum, witch hazel, tannic acid, and pharmaceutical preparations such as silver nitrate and zinc compounds.