Often hives are caused by an adverse reaction to some food or durg. Foods likely to cause hives include nuts, tomatoes, shellfish, and berries. Drugs often responsible for producing hives are penicillin, sulfa, anticonvulsants, phenobarbital and aspirin.
A small percentage of cases are classified as the physical urticarias. Cholinergic urticaria describes those hives that develop following activities which increase the body’s temperature and with exposure to warmth or heat. Cold-induced urticaria occurs after exposure to cold wind or water. Another type of physical urticaria is solar urticaria caused by exposure to sunlight or to a sun lamp.
Exercise is another common cause of hives in which there is no allergic substance involved. Those individuals affected can also develop respiratory obstruction and/or lose consciousness. Such a severe reaction is called exercise-induced anaphylaxis. It has been recently appreciated that the combination of exercise and consumption of a food can together cause hives or anaphylaxis whereas individually exercise or the food is harmless.