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'Astringent' medicines cause shrinkage of mucous membranes or exposed tissues and are often used internally to check discharge of blood serum or mucous secretions. This can happen with a sore throat, hemorrhages, diarrhea, or with peptic ulcers. Externally applied astringents, which cause mild coagulation of skin proteins, dry, harden, and protect the skin. Acne sufferers are often advised to avoid astringents, which are believed to worsen the clogging of pores (see Witch Hazel). Astringents also help heal stretch marks and other scars. Mild astringent solutions are used in the relief of such minor skin irritations as those resulting from superficial cuts, allergies, insect bites, or fungal infections such as athlete's foot.
Some common astringent agents include alum, oatmeal, yarrow, witch hazel, bayberry, very cold water, and rubbing alcohol. Astringent preparations include silver nitrate, zinc oxide, zinc sulfate, Burow's solution, tincture of benzoin, and vegetable substances such as tannic and gallic acids. Some metal salts and acids have also been used as astringents.