urticaria

n. skin condition that is caused by an allergic reaction and is characterized by raised red patches on the skin accompanied by itching, hives

Urticaria (or hives) is a skin condition, commonly caused by an allergic reaction, that is characterized by raised red skin welts. It is also known as nettle rash or uredo. Welts from hives can appear anywhere on the body, including the face, lips, tongue, throat, and ears. Welts may vary in size from about 5 mm (0.2 inches) in diameter to the size of a dinner plate; they typically itch severely, sting, or burn, and often have a pale border. Urticaria is generally caused by direct contact with an allergenic substance, or an immune response to food or some other allergen, but can also appear for other reasons. The rash can be triggered by quite innocent events, such as mere rubbing, or exposure to cold.
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Urticaria /ur·ti·ca·ria/ hives; a vascular reaction of the upper dermis marked by transient appearance of slightly elevated patches which are redder [more]Urticaria - Community and Resources

Noun
1. an itchy skin eruption characterized by weals with pale interiors and well-defined red margins; usually the result of an allergic response to insect bites or food or drugs
(synonym) urtication, hives, nettle rash
(hypernym) rash, roseola, efflorescence, skin rash

n. urticaria, skin condition that is caused by an allergic reaction and is characterized by raised red patches on the skin accompanied by itching, hives