Definition

Hives are small, itchy, red swollen areas on the skin. The swelling occurs singularly or in clusters. Hives tend to fade after a few hours, but new ones can appear. Most cases go away within a few days. However, some last a few weeks or longer.

Hives © Nucleus Medical Media, Inc.

Causes

Hives are often caused when the body releases a chemical called histamine. Histamine is released during an allergic reaction. Many people, though, get hives without being exposed to something they are allergic to.

While the cause is unknown in some cases, these factors may cause hives:

• Foods, most commonly:
  • Eggs
  • Shellfish
  • Nuts
  • Chocolate
  • Fish
  • Tomatoes
  • Fresh berries
  • Milk
• Medicines
• Reaction to allergy shots
• Infections
• Insect bites or stings
• Latex
• Pressure
• Cold or heat
• Sunlight
• Pollen
• Stress
• Underlying medical conditions:
  • Vasculitis (inflammation of the blood vessels)
  • Thyroid disease—hypothyroidism or hyperthyroidism
  • Some cancers, such as lymphoma
  • Viral infections, such as HIV infection, hepatitis, and cytomegalovirus

Risk Factors

Factors that may increase your chances of hives include:

• Exposure to an allergen—something that causes an allergic reaction
• Exposure to an allergen that triggered hives in the past

Symptoms

Symptoms of hives can vary from mild to severe:

• Itchiness
• Redness
• Swelling
• Excessive swelling of the eyelids, lips, or genitals
• Burning
• Stinging
• Difficulty breathing or swallowing— Call for emergency services right away if you are having these symptoms.

Diagnosis

You will be asked about your symptoms and medical history. A physical exam will be done. You may need to see a doctor who specializes in skin disorders (dermatologist) or allergies (allergist).

Your bodily fluids and tissues may be tested. This can be done with:

• Blood tests
• Skin prick test
• Skin biopsy

Images may be taken of your bodily structures. This can be done with x-rays.

Treatment

The best way to treat hives is to find and then avoid the cause.

If the cause cannot be found, there are medicines to reduce symptoms or treat hives:

• Antihistamines
• Leukotriene antagonists
• Oral steroid medications for hives resistant to other treatments
• Anti-inflammatory medicines
• Immunosuppressant medicines
• Ultraviolet light therapy
• Prescription epinephrine (adrenalin) injections for cases when swelling affects the airways

Prevention

The best way to prevent hives is to avoid the allergen that caused you to get hives in the past.