Are Hives Always Caused by an Allergy?
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Hives are swollen, red or pink bumps, patches, or welts on the skin that usually appear suddenly. Itching is the most common symptom associated with 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 histamineis released by specialized cells known as mast cells. It is true that allergic reactionsultimately 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 stressand 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.