Astringent

An astringent substance is a chemical substance that tends to shrink or constrict body tissues, usually locally after topicalmedicinal application. The word "astringent" derives from Latinastringere, meaning "to bind fast". Two common examples are calamine lotionand witch hazel. Astringency is also the dry, puckery sensation caused by tanninin some wines. The tannins denature the salivary proteins, causing a rough "sandpapery" mouthfeel. A small amount of astringency is expected in some wines, especially young red wines made from powerful varieties such as cabernet sauvignon.

Astringent substances are also found in many fruitssuch as blackthorn, bird cherryand persimmonfruits, giving them their mouth-puckering qualities. Astringency is tasted as unpleasant by many mammals(including humans), which tend to avoid eating astringent fruit; conversely, birdsdo not taste astringency and readily eat these fruit. It is thought that fruit astringency evolved in plants because birds are better than mammals at long-distance seeddispersal (often flying some distance before passing the seeds in their droppings), so plants that contained astringent substances in the fruit are more successful than those that did not.

Astringent medicines cause shrinkage of mucous membranesor exposed tissues and are often used internally to check discharge of blood serumor 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. Acnesufferers are often advised to avoid astringents, which are believed to aid in clogging pores. Mildly astringent solutions are used in the relief of such minor skin irritations as those resulting from superficial cuts, allergies, insectbites, or fungal infections such as athlete's foot.

Some common astringent agents include alum, oatmeal, very cold water, and rubbing alcohol. Astringent preparations include silver nitrate, zinc oxide, Burow's solution, tincture of benzoin, and vegetable substances such as tannicand gallic acids. Some metal saltsand acids have also been used as astringents.

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It uses material from the http://en.wikipedia.org/wiki/Astringent Wikipedia article Astringent.