Are Hives Always Caused by an Allergy?
Hives are swollen, red or pink bumps, patches, or welts on the skin that usually appear suddenly and may change from one location to another on the body. Itching is the most common symptom of hives, although some people report that hives cause a stinging or burning sensation. Hives are a very common reaction to all kinds of stimuli. While an allergic reaction can be a cause of hives, in the majority of outbreaks, the exact cause of hives is not known. Hives are also known as urticaria.
Hives form when a chemical called histamine is released by specialized cells known as mast cells. It is true that allergic reactions ultimately lead to the release of histamine, but other circumstances can result in the release of histamine, causing an outbreak of hives. Histamine acts by causing blood vessels to leak fluid into the nearby tissues. In the skin, small areas of swelling develop as a result of capillary (the smallest blood vessels) leakage.
In addition to allergic reactions to medications, foods, or other substances, hives may be triggered by direct physical stimulation such as temperature extremes, water, sun, and physical exercise. Having a viral infection can also cause an outbreak of hives, and even stress and nervousness have been associated with hives outbreaks. In the form of hives known as dermographia, or "skin writing," raised, itchy red welts with adjacent flares appear wherever the skin is scratched or where belts and other articles of clothing rub against the skin.