Definition

Hives are small, itchy, red swellings 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 © 2011 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 (desensitization shots)
• Infections
• Insect bites or stings
• Latex
• Pressure
• Cold or heat
• Sunlight
• Thyroid disease ( hypothyroidism, hyperthyroidism)
• Pollen
• Stress
• Vasculitis (inflammation of the blood vessels)

Risk Factors    TOP

A risk factor is something that increases your chance of getting hives. Tell your doctor if you have any of these:

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

Symptoms    TOP

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 911 if you are having these symptoms.

Diagnosis    TOP

The doctor will ask about your symptoms and medical history, and do a physical exam. You may need to see a doctor who specializes in skin disorders (dermatologist) or allergies (allergist). The following tests will be done:

• Skin prick test —a tiny bit of an allergen is placed in your skin with a needle to see if the area becomes raised or irritated
• Skin biopsy —a small portion of abnormal skin is removed
• X-ray —a test that uses radiation to take a picture of structures inside the body, especially bones
• Blood tests

Treatment    TOP

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

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

• H1-blocking medicines like:
  • Diphenhydramine (eg, Aler-Cap, Benadryl Allergy)
  • Hydroxyzine (eg, Vistaril)
  • Cyproheptadine
  • Fexofenadine (eg, Allegra)
  • Loratadine (eg, Claritin)
  • Acrivastine (eg, Semprex)
  • Cetirizine (eg, Zyrtec)
  • Doxepin (eg, Prudoxin, Sinequan, Zonalon)
  • Levocetirizine (eg, Xyzal)
• H2 blocking medicines like:
  • Cimetidine (eg, Tagamet HB)
  • Ranitidine (eg, Zantac)
  • Famotidine (eg, Pepcid)
• Leukotriene antagonists like Montelukast
• Oral steroid medications (eg, prednisone) 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    TOP

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