Hives are small, red swellings on the skin, occurring singularly or in clusters. They tend to fade away after a few hours, but new ones can appear. Most cases of hives resolve within a few days, but some can take a few weeks.

Causes

Hives are caused by a reaction in which certain cells of the body release a substance called histamine, a substance released by many cells during an allergic reaction. Many people, however, develop hives without any possible exposure to allergy-producing substances. In fact, the cause of a hive reaction is often unknown, but it may include:

• Foods, most commonly:

• • Eggs

• • Shellfish

• • Nuts

• • Chocolate

• • Fish

• • Tomatoes

• • Fresh berries

• • Milk

• Medications

• Reaction to allergy shots (desensitization shots)

• Infections

• Insect bites or stings

• Latex

• Pressure

• Cold

• Sunlight

• Thyroid disease

• Pollen

• Stress

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Exposure to anything that produces an allergic reaction (ie, an allergen) can increase your risk of hives. Also, situations that have produced hives in the past often produce them again.

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 (Seek immediate medical care if you have these symptoms.)

Diagnosis

The doctor will ask about your symptoms and medical history, and perform a physical exam. You may be referred to a doctor who specializes in skin disorders (dermatologist) and/or allergies (allergist). To help determine if your hives are related to certain allergies, a skin prick test may be done. To perform this test, your doctor places a tiny bit of an allergen in your skin with a needle and watches to see if the skin in that area becomes raised or irritated.

Treatment

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

Since this is often not possible, there are a number of medications for treating hives:

• Over-the-counter antihistamines such as:

• • Diphenhydramine

• • Hydroxyzine

• • Cyproheptadine

• Prescription antihistamines such as:

• • Fexofenadine (Allegra)

• • Loratadine (Claritin)

• • Acrivastine (Semprex)

• • Cetirizine (Zyrtec)

• H2 blocking medications such as:

• • Cimetidine

• • Ranitidine

• • Famotidine

• Anti-inflammatory medications

• Steroid skin creams

• Oral steroid medications (prednisone) for hives resistant to other treatments

• Prescription epinephrine (adrenalin) injections for cases when swelling affects the airways

Prevention

The best way to prevent hives is to avoid substances or situations that have caused you to get hives in the past.

Resources:

American Academy of Allergy, Asthma, and Immunology
http://www.aaaai.org

American Academy of Dermatology
http://www.aad.org

CANADIAN RESOURCES:

Canadian Dermotology Association
http://www.dermatology.ca/english/

Dermatologists.ca
http://www.dermatologists.ca/index.html

References:

American Academy of Allergy, Asthma, and Immunology website. Available at: http://www.aaaai.org.

American Academy of Dermatology website. Available at: http://www.aad.org.

National Institute of Arthritis and Musculoskeletal and Skin Diseases website. Available at: http://www.niams.nih.gov/.