The body's immune system is designed to produce various factors to fight foreign substances, including bacteria and viruses that the immune system perceives as threatening. An allergic response occurs when the body's immune system over-responds, or is hypersensitive to particles known as allergens. Common allergens include plant pollens, molds, dust mites, animal dander, industrial chemicals, food, medicines and insect venom. More than 10% of people get hives.
Important components of the immune system are the antibodies produced by lymph tissue. A key player in the allergic response is the antibody known as immunoglobulin E (IgE). IgE is overproduced in certain people, usually those with inherited susceptibility.
During an allergic attack, these antibodies attach to cells known as mast cells, which are generally concentrated in the lungs, skin and mucous membranes. Once IgE binds to mast cells, these cells are programmed to release a number of chemicals. One of these chemicals, histamine, opens the blood vessels and causes skin redness and swollen membranes. Histamine causes many of the symptoms associated with allergies. Hives are a common allergic reaction involving the skin.