Hives are raised, itchy welts on the surface of the skin caused by hypersensitivity to a substance. When the body encounters a substance that it is allergic or sensitive to, it releases histamines and other chemicals into the bloodstream. As a result, the capillaries and tiny veins leak. The leaking fluid gets trapped in the skin and lining membranes, which causes the localized swelling seen with hives. The welts, which are also called wheals, may remain small, or may spread large enough to join together. With hives, the center of the welt blanches, or turns white, when pressed.

When hives occur around the face, particularly around the lips and eyes, they are called angioedema. Angioedema may also occur on the hands, feet and throat. Hives can come and go suddenly, often without any apparent cause. It is estimated that up to 70% of hives go undiagnosed as to the cause, because they can appear hours after exposure to the irritant.

Up to 20% of people will have hives at some point in their lives, but surprisingly, girls are more prone to hives than boys. Family history also plays a part in determining whether a person is inclined to developing hives. If you have a genetic tendency to allergies or food sensitivities, chances are that you may develop hives sometime.

Hives are a manifestation of an inflammatory response of the body. Substances which trigger hives can come from many different sources. Common triggers include medicine, food, contact irritants, infection or illness, environment and stress.

Medicines, such as antibiotics, often trigger hives. Food such as shellfish, fish, eggs, milk, nuts, berries and food additives are the most common histamine triggers. Some contact irritants which can bring on a reaction include animal dander, moth scales, animal saliva and insect bites and stings.

Inhaled irritants also can cause hives — this is often common with people who suffer from hay fever. Mold and pollen are other inhaled allergens that may cause hives. Illnesses, infections and parasites such as mononucleosis, strep and giardia can cause an inflammatory response as well.

There are several other physical causes of hives, or uticaria, as doctors call them. These include cold uticaria, which are hives caused by contact with cold water or air. Dermatographia is a more rare cause of hives, affecting only 5% of people. People who suffer from dermatographia get hives by simply rubbing or stroking their skin.

Pressure uticaria is caused by tight clothing or jewelry. Heat, exercise or emotional stress can cause cholinergic uticaria. Aquagenic uticaria results from exposure to sweat and water. One of the rarest forms of hives is solar uticaria, which is caused by exposure to the sun.

Although hives are can vary as to how itchy they are, they are usually uncomfortable to experience. Hives are harmless, but they can indicate a serious allergy or underlying illness. Chronic uticaria should be investigated by your physician.

Complications of hives can include anaphylaxis, which is a swollen airway. This can be the result of a serious allergy and should be treated immediately. Symptoms of a serious reaction include tightness in the throat, shortness of breath, swelling of the tongue or face, wheezing and loss of consciousness.

Home treatments for hives include over the counter anti-itch cream and antihistamines such as Benadryl. For those who seek the treatment of a doctor, Atarax, a more powerful antihistamine, may be prescribed. Newer antihistamines with H2 blockers such as Cimetidine have proved useful in the treatment of allergies and the resulting hives.