Hives

Hives (urticaria) - close-up

Hives develop when histamine is released into the small blood vessels (capillaries). The capillaries dilate which causes a welt, and fluid oozes into the surrounding tissue, causing swelling. Histamine also causes intense itching.

Also known as: Urticaria

Definition

Hives are raised, often itchy, red welts on the surface of the skin. They are usually an allergic reaction to food or medicine.

Causes, incidence, and risk factors

When you have an allergic reaction to a substance, your body releases histamine and other chemicals into your bloodstream. This causes itching, swelling, and other symptoms. Hives are a common reaction, especially in people with other allergies such as hay fever.

When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema. Swelling from angioedema can also occur around your hands, feet, and throat.

Many substances can trigger hives, including:

  • Animal dander (especially cats)
  • Insect bites
  • Medications
  • Pollen
  • Shellfish, fish, nuts, eggs, milk, and other foods

Hives may also develop as a result of:

  • Emotional stress
  • Extreme cold or sun exposure
  • Excessive perspiration
  • Illness (including lupus, other autoimmune diseases, and leukemia
  • Infections such as mononucleosis

Symptoms

  • Itching
  • Swelling of the surface of the skin into red- or skin-colored welts (called wheals) with clearly defined edges

The welts may get bigger, spread, and join together to form larger areas of flat, raised skin.

They can also change shape, disappear, and reappear within minutes or hours.

The welts tend to start suddenly and go away quickly. When you press the center of a red welt, it turns white. This is called blanching.

Signs and tests

Your doctor can tell if you have hives by looking at your skin.

If you have a history of an allergy, then the diagnosis is even more obvious.

Occasionally, skin or blood tests are done to confirm that you had an allergic reaction and to test for the substance that caused the allergic response.

Treatment

Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:

  • Avoid hot baths or showers.
  • Avoid irritating the area with tight-fitting clothing.
  • Take antihistamines. Diphenhydramine is considered the most effective.

If your reaction is severe, especially if the swelling involves your throat, you may require an emergency shot of epinephrine (adrenaline) or steroids. Hives in the throat can block your airway, making it difficult to breathe.

Expectations (prognosis)

Hives may be uncomfortable, but they generally are harmless and disappear on their own. In most cases, the exact cause of hives cannot be identified.

Complications

  • Anaphylaxis (a life-threatening, whole-body allergic reaction that causes breathing difficulty)
  • Swelling in the throat can lead to life-threatening airway blockage

Calling your health care provider

Call 911 or your local emergency number if you have:

  • Fainting
  • Shortness of breath
  • Tightness in your throat
  • Tongue or face swelling
  • Wheezing

Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care measures.

Prevention

  • Avoid exposure to substances that give you allergic reactions.
  • Don't wear tight-fitting clothing and avoid hot baths or showers just after an episode of hives. These can both cause the hives to return.

References

Amar SM. Uticaria. Prim Care. March 1, 2008; 35(1): 141-57, vii-viii.

Habif TP. Clinical Dermatology. 4th ed. St. Louis, Mo: Mosby; 2004.

See also:

  • Disease

    Angioedema

    Angioedema is a swelling, similar to hives, but the swelling is beneath the skin rather than on the surface. Hives are often called welts. They are a surface swelling. It is also possible to have angioedema without hives. See also:

  • Disease

    Autoimmune disorders

    Graves' disease

    An autoimmune disorder is a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue. There are more than 80 different types of autoimmune disorders. See also:

  • Disease

    Mononucleosis

    Mononucleosis, photomicrograph of cells

    Mononucleosis is a viral infection causing fever, sore throat, and swollen lymph glands, especially in the neck. See also: (acute CMV infection)

  • Disease

    Anaphylaxis

    Shock

    Anaphylaxis is a life-threatening type of .

Review date:
April 15, 2009
Reviewed by:
Kevin Berman, MD, PhD, Associate, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network.
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