nettle rash, an allergic reaction characterized by the sudden and rapid appearance on the skin (sometimes also on the laryngeal mucosa) of intensely itching wheals.
Urticaria is often caused by the sting of the nettle and certain other plants. Insect bites, temperature, and chemical agents are also among its causes. Other factors include parasitic worms, chronic constipation, liver and kidney diseases, and allergic sensitivity to some foods (for example, strawberries, citrus fruits, eggs, mushrooms, preserves, certain fish, pork, and chocolate). Urticaria is sometimes caused by hypersensitivity to drugs (especially to those of chemical origin). The rash associated with the condition is a manifestation of the inflammatory reaction and edema of the skin that result from a sudden increase in the permeability of the capillaries in the area. This results from the liberation of histamine from the mast cells of the skin by allergic alteration. Urticaria usually disappears without a trace within a few hours, although it sometimes recurs. It is treated by purgation (by enemas, laxatives), special diet (mostly milk and vegetables, with limited salt intake), and desensitizing and anti-histaminic agents.
R. S. BABAIANTS