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 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.
Most outbreaks of hives resolve on their own. The hives may last for just a few minutes, a few hours, or they may persist for days. Treatment of hives is directed toward relieving the unpleasant symptoms, mainly itching. Over-the-counter or prescription antihistamine medications are useful in relieving the itch, and creams or ointments that contain antihistamines or medications that reduce signaling from the nerve endings in the affected skin can also provide relief. In addition to medications, applying cool compresses to the affected area and wearing light, loose-fitting clothing can help ease the discomfort of hives.
Longo, Dan, et al. Harrison's Principles of Internal Medicine. 18th ed. McGraw-Hill Professional, 2011.