In others exercise and sweating, or applying ice to the skin can cause welts. Less commonly, hot water, sunburn, or pressure on the skin can cause hives. Foods which often cause this problem include fish, nuts, berries, eggs, and shellfish. Food dyes or preservatives can also be culprits. Insect stings causing hives usually come from bee, wasp, hornet or yellow jacket stings.
Some people get hives from inhaling pollen, or animal dander.
Chronic urticaria is more likely to be caused by certain infections, such as mononucleosis, strep or hepatitis, or other, more complicated and possibly serious internal diseases. Extensive medical tests are rarely required for acute urticaria. The trigger is often obvious and the condition disappears, or is easily treated. Antihistamines make the hives less itchy, though they may not make them disappear any faster. Many antihistamines, such as Benadryl and Chlor-Trimeton are easily obtained without a prescription.