Urticaria
Alternative names:
hives
Definition:
Raised red welts of various size on the surface of the skin, often itchy, associated with an allergic reaction and histamine release or abnormalities in the complement system or the kinin system (parts of the immune system).
Causes, incidence, and risk factors:
About 1 out of 5 people experience urticaria (hives) at some time. Hives are more common in people who have experienced other allergic reactions, including hay fever and angioedema. The welts occur on the surface of the skin, usually in batches. Release of histamine and other chemicals into the bloodstream, associated with the allergic response, causes the itching, localized swelling, and other symptoms.
Many substances, called allergens, can trigger an allergic response resulting in hives. Common allergens include: - medications
- foods (such as berries, shellfish, fish, nuts, eggs, milk, and others)
- pollen
- animal dander (especially cats)
- insect bites
- exposure to water, sunlight, cold or heat
- emotional stress
Hives may also develop after infections or illness (including autoimmune diseases, leukemia, and others). There seems to be a hereditary tendency toward the development of hives.
Some nonallergic causes of hives include:
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