s impossible to find out exactly why
hives have formed. The most common foods that cause
hives are nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk. Certain food additives and preservatives may also be to blame.
Hives caused by direct physical stimulation of the skin -- for example, cold, heat, sun exposure, vibration, pressure, sweating, and exercise is called physical urticaria. The hives usually occur right where the skin was stimulated and rarely appear elsewhere.