Hives are red, itchy welts on the skin that come and go over the course of minutes or hours. All types of hives can cause itching. They usually form on the skin but sometimes hives form in the soft tissue of the mouth, eyes and throat. Hives are the result of an allergic reaction in the skin. They are caused by the release of histamine.
Histamine is released when a person's immune system tries to fight a foreign substance.
The release of histamine causes inflammation in the skin. Hives are characterized by itchy red welts and swelling of facial features. Hives can cause a reaction that involves the whole body, not just the skin. This is called anaphylaxis . There are several known factors that cause histamines to be released, and hives to form.