Cholinergic Urticari. Cholinergic urticaria is a subcategory of physical urticaria(aka hives) that is a skin rash brought on by a hypersensitive reaction to body heat. Symptoms follow any stimulus to sweat such as exercise (sometimes called exercise-induced urticaria, heat from the sun (which could also indicate solar urticaria), saunas, hot showers (reaction to water).
Heat Assoc Hives. Cholinergic urticaria is a type of hives brought on by heat inducing stimuli. Meaning, it causes small 2-3 mm hive-like bumps symmetrically on the body after something is done to increase the body's core temperature. Exercise, hot weather, spicy foods, and alcohol can all bring on an episode. It usually happens in young people, and is rare in the elderly. The hives are very itchy.