Urticaria (commonly called welts or hives) is an itchy, raised, red rash, which may occur on any part of the body. Hives vary in size from a few millimeters to as large as a pancake, but rarely cover an entire portion of the body. Hives may last from minutes to hours (but usually not more than 24 hours) and may recur daily or only once in a while. Hives occur when histamine and other inflammatory chemicals are released from white blood cells (called mast cells) in the skin.
Acute urticaria may be caused by allergic reactions to foods, medications, insect stings, or another allergenic substance. Allergic hives start within minutes of exposure and tend to recur with future exposures. Allergic hives may be accompanied by other systemic allergic symptoms like wheezing, swelling in the throat or low blood pressure (anaphylaxis). Hives may also occur with physical stimuli such as cold, heat, and pressure, or during emotional stress or with viral illnesses. In fact, viral illness is the most common cause of acute urticaria in children.
Chronic urticaria refers to hives occurring, on most days of the week, for more than 6 weeks. A cause for chronic urticaria is found in less than 5% of cases. Allergic reactions are not known to cause chronic urticaria and allergy tests are usually not helpful. However, in some patients chronic hives may be related to thyroid disease or systemic autoimmunity. Blood work is often ordered to check for these conditions as a possible cause of the hives.
Angioedema (swelling) often accompanies hives and may be subtle to sometimes large and distorting. Eyelids, lips, extremities, and genitals are common sites of swelling. An allergy evaluation can help to identify factors that may be responsible for the hives. Evaluation can also help to determine factors that are not associated with the hives. This may help to reduce the need for an overly restrictive diet. When the precise cause of hives is identified, recurrence can be prevented by avoiding the stimulus. When no cause is found, or avoidance is not effective or feasible, control of hives can often be accomplished with the use of antihistamine medications that your doctor will recommend.
The following are common triggers in people who suffer from chronic hives:
- Aspirin and aspirin-like medications (Advil, ibuprofen, Motrin, Aleve, etc.) may aggravate chronic hives in more than 50% of cases. Aspirin may be found in many cold and headache preparations (Alka Seltzer, Excedrin, etc.), so be sure to read the label carefully. When hives are active, acetaminophen (Tylenol) may be used as a substitute for aspirin.
- Scratching the skin usually causes more itching and swelling. You should avoid anything which causes itching (tight fitting clothing, wool, drying soaps, etc.).
- Heat often worsens hives. Prolonged hot baths and showers should be avoided.
Xolair (omalizumab) is an anti-IgE antibody recently approved for treatment of chronic hives. Xolair is given once monthly as a subcutaneous injection in the office, followed by an observation period. It is reserved for hives that do not respond to maximal medical treatment. Xolair injections can rarely cause an allergic reaction.