Urticaria (hives)

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

Causes, incidence, and risk factors

Hives are very common, especially in people who have experienced other allergic reactions, like hay fever, and are sometimes hereditary. When you have an allergic reaction to any substance, histamine and other chemicals are released into your bloodstream. These chemicals cause itching, swelling, hives, and other symptoms.

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 an allergic response resulting in hives, such as:

Medications
Foods (berries, shellfish, fish, nuts, eggs, milk, and others)
Pollen
Animal dander (especially cats)
Insect bites

Hives may also develop from:

Infection (like mononucleosis) or illness (including lupus and other autoimmune diseases, leukemia, and others)
Emotional stress
Extreme cold or sun exposure
Excessive perspiration

Symptoms

Itching
Swelling of the surface of the skin into red or skin colored welts (called wheals) with clearly defined edges
The welts may enlarge, 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 resolve quickly. When you press the center of a red welt, it blanches (turns white).

Signs and tests

Your doctor can tell if you have hives by the appearance of your skin. If you have a history of an allergy, then the diagnosis is even more obvious. Occasionally, skin or blood tests are performed to confirm that this was an allergic reaction and to test for the substance that caused your allergic response.

Treatment

Treatment may not be needed if hives are mild. They may disappear on their own. Some steps that you can take to reduce itching and swelling include:

Apply cool compresses to the part of your body with welts. This may reduce swelling and pain. If a large part of your body is affected, soak in a cool bath. Avoid hot baths or showers.
Avoid irritating the area with tight-fitting clothing.
Apply Calamine lotion.
Take antihistamines like diphenhydramine (Benadryl). If over-the-counter antihistamines make you too drowsy, talk to your doctor about non-sedating antihistamines.

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

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
Life-threatening airway obstruction, if swelling occurs in the throat

Calling your health care provider

Call your local emergency number (such as 911) if you experience any of the following:

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

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

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 precipitating factors may cause the hives to return.