Author: Glossary
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Urushiol
The principal toxic irritant substance of plants such as poison ivy, which produces characteristic severe dermatitis on contact.
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Urticate
To produce urticaria.
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Solar pigmentosa
Urticaria occurring in certain people after exposure to sunlight.
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Pressure pigmentosa
Urticaria produced by pressure perpendicular to the surface of the skin. The persistent red swelling appears after a delay of 1 to 4 hr.
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Physical urticaria
Urticaria due to the direct effects of physical forces on the skin. Cold temperature (cold urticaria), pressure (pressure urticaria), ultraviolet radiation (solar urticaria), and scratching (dermographism) are some causes of physical urticaria.
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Papular urticaria
Urticaria in which the wheal is followed by a lingering papule and considerable itching. It is most commonly observed in debilitated children.
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Urticaria medicamentosa
Urticaria caused by an allergic reaction to a drug (e.g., a sulfa drug).
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Urticaria factitia
Urticaria following slight irritation of the skin.
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Cold urticaria
Cold-induced urticaria that may progress to angioedema.
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Chronic urticaria
Urticaria that occurs frequently for 6 weeks or more. It is often associated with autoimmune disease.