Urticaria (Hives) and Angioedema

Urticaria (commonly known as hives) is a skin rash characterized by red, raised itchy patches. They are often intensely itchy. They are typically small, but several patches may join together to form larger plaques. Urticaria are caused by the leakage of plasma from the small blood vessels close to the skin in response to a chemical called histamine, which is produced by specialized cells called mast cells. They usually appear on covered areas of the skin such as the trunk, back and upper arms and legs; however, they can also involve the neck and face.

Up to 20 percent of people will experience a case of hives in their lifetimes. Hives usually last from a few minutes to six hours and as old hives resolve, new ones appear. A case of hives typically lasts up to a few days.

Angioedema is similar to hives, except that it is caused by the leakage of plasma from blood vessels deeper in the skin. As a result, angioedema causes severe swelling, usually around the eyes and mouth, but more dangerously inside the throat, tongue, or airways—sometimes causing difficulty breathing. It can arise in conjunction with hives, but usually appears alone and is less common.

Chronic urticaria includes cases of hives that last more than six weeks. For almost 90 percent of patients with chronic urticaria, the cause is never identified. One-third of all cases of hives are chronic, and in contrast to acute urticaria, these hives are rarely caused by allergies. A few people with chronic urticaria are found to have autoimmune diseases (particularly autoimmune thyroiditis or Hashimoto’s disease).

Acute urticaria and angioedema are often caused by specific triggers and it is important to try to identify these triggers in order to prevent future outbreaks. Many drugs can trigger hives, including antibiotics (particularly penicillins and sulfa antibiotics), painkillers or opiates (e.g., morphine and codeine), oral contraceptives, aspirin and NSAIDS (such as ibuprofen) and intravenous contrast dye used in medical procedures such as CT scans. Food allergies can trigger hives—most commonly milk, peanuts, eggs and wheat in children, and shellfish, peanuts and other fish in adults.

Eighty percent of all cases of urticaria in children are caused by viruses, typically a week or two after the illness begins. Insect stings are common causes of hives localized to the area of the sting. Widespread hives associated with shortness of breath and swelling of the throat are characteristic of anaphylaxis—a different condition—and should prompt immediate medical attention. Physical contact with certain allergens—typically animal saliva, plant juices and latex—are also common causes of urticaria. Emotional and physical stress may also play a role.

The best treatment for hives and angioedema is to identify and avoid the trigger; however, this is not always possible. Antihistamines block the blood vessels’ response to histamine and thus prevent the release of plasma that causes hives and angioedema. One family of antihistamines (H1 blockers) includes drugs like Benadryl and Vistaril and can be very effective, but also may cause drowsiness. A second generation of H1 blockers—including Claritin and Zyrtec—is less likely to cause drowsiness. A second family of antihistamines (H2 blockers including Pepcid and Zantac) is usually used for gastrointestinal problems but may be helpful here. Prednisone is sometimes effective for difficult cases but should be generally avoided because of side effects. Try cool compresses or baths, avoid direct sunlight and wear loose-fitting clothing. Avoid activities that may cause sweating. Contact your doctor immediately if you have difficulty breathing, wheezing, or swelling of the tongue, lips or face.

Dr. McMahon, a graduate of Yale University and the University of Pittsburgh School of Medicine, is board certified in Internal Medicine. She is a member of the American College of Physicians and the Allegheny and Pennsylvania Medical Societies. She is in solo practice in the North Hills.