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Hives, urticaria, nettle rash or welts

Hives, also known as urticaria, welts or nettle rash, is a itchy, raised rash on the skin.

The hives usually appear suddenly, sometimes because of an allergic reaction or being stung by a nettle.

Photo of Hives (Urticaria) Skin Rash

Image: © Scott Camazine / Phototake -- All rights reserved.

Hives usually cause itching, but may also cause burning or stinging. They can appear anywhere on the body, including the face, lips, tongue, throat or ears. Hives vary in size (from a pencil rubber to a dinner plate), and may join together to form larger areas known as plaques. They usually last for less than 24 hours, but in some case they can last for several days or months before fading.

Angioedema is similar to urticaria, but the swelling occurs beneath the skin instead of on the surface. Angioedema is characterised by deep swelling around the eyes and lips and sometimes of the genitals, hands and feet. It generally lasts longer than urticaria, but the swelling usually goes away with 24-72 hours.

Occasionally severe, prolonged tissue swelling can be disfiguring. Rarely angioedema of the throat, tongue or lungs can block the airways, causing difficulty breathing. This may become life threatening.

What causes hives and angioedema?

Hives and angioedema form when, in response to histamine, blood plasma leaks out of small blood vessels in the skin. Histamine is a chemical released from specialised cells along the skin's blood vessels.

Allergic reactions, chemicals in foods, insect stings, sunlight exposure or medicines can all cause histamine release. Sometimes it's impossible to find out exactly why hives have formed.

There are several different types of hives and angioedema including:

  • Acute urticaria and/or angiodema: Hives or swelling lasting less than six weeks. The most common causes are foods, medicines, latex or infections. Insect bites and internal disease may also be responsible. The most common foods that cause hives are nuts, chocolate, fish, tomatoes, eggs, fresh berries, soya, wheat and milk. Fresh foods cause hives more often than cooked foods. Certain food additives and preservatives may also be to blame. Medicines that can cause hives and angioedema include aspirin and other non-steroidal anti-inflammatory medications such as ibuprofen, some high blood pressure medications and some painkillers such as codeine.
  • Chronic urticaria and/or angioedema: Hives or swelling lasting more than six weeks. The cause of this type of hives is usually more difficult to identify than those causing acute urticaria and/or angioedema. The causes can be similar to those of acute urticaria but can also include autoimmunity, chronic infections, hormonal disorders and malignancy.
  • Physical urticaria: Hives caused by direct physical stimulation of the skin - for example cold, heat, sun exposure, vibration, pressure, sweating and exercise. The hives usually occur directly where the skin was stimulated and rarely appear anywhere else. Most of the hives appear within one hour after exposure.
  • Dermatographism: Hives that form after firmly stroking or scratching the skin. These hives can also occur along with other forms of urticaria.
  • Hereditary angioedema: This is painful swelling of tissue. It is passed on through families.

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