ALLERGY is a type of reaction that can vary from annoying to fatal. The question has always been: what possible utility to the body does the allergic reaction, which has survived evolution, provide? The best theory fingers parasitic infestations; not only can parasites cause allergic reactions, Indicate allergy by showing blood eosinophilia, but the allergic reaction seem to help us fight parasitic infestation, which was much more common in humanity’s past, and in present day underdeveloped societies.
URTICARIA consists of a number of little welts or bumps that pop up on the skin and are very itchy. This reaction is caused by little darkly-staining cells called MAST CELLS, which release Histamine and other irritants into the skin, causing hives. These mast cells are provoked into releasing their irritating cargo by IGE antibodies, the basis of true allergy.

Treatment consist of removing the cause, blocking the action of the IgE antibodies, or giving medication to block the action of the histamine( anti-histamines).
There are multiple common causes, several giving its name to a type of Urticaria. Pressure urticaria can be caused by a belt or tight fitting clothing pressing on the skin to cause the hives. Solar urticaria can be caused by sunlight.
Cold urticaria can be caused by exposure to very cold objects. Hives can also be caused stress, exercise, different foods(seafood and strawberries are the most famous), different drugs(penicillin and aspirin are the most famous), and scratching on the skin(dermatographia).
Hives can occur as a feature of ANAPHYLAXIS. If the IgE-mast cell reaction is extensive, the blood pressure can drop, internal organs can be affected, and emergency treatment must take place to prevent death.
My only experience with hives was after a bee sting, when I broke out with itchy bumps. I had desensitization with honeybee venom, although this is not always done these days. Be sure to check with your doctor if you have such a reaction, however.
The biggest recent improvement in treating people who are incapacitated with frequently recurring and long lasting hives is anti-IGE, an expensive but very effective injection.
If you have hives, be sure to keep a record of events that immediately preceded the hives, including foods, activities,, and exposures. Although the recommended Mayo clinic article that follows suggests that you see a dermatologist or an allergist, I would reverse that and suggest the allergist first.