Cholinergic urticaria is a subcategory of physical urticaria (aka hives) that is a skin rash brought on by a hypersensitive reaction to boy 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 can also indicate water urticaria), spicy foods which may cause an increase in body temperature or even stress due to blushing or anger. Some people only have symptoms during the winter months where their body temperature rises when it is unacclimatized to heat.