|Allergy and Asthma
Southwestern United States
||Information for patients with allergy and related
in the Southwest
Hives (urticaria) and angioedema
Urticaria is an itchy rash consisting of inflamed wheals (welts) that are raised above the level of the surrounding skin. The wheals vary in size and shape, and tend to come and go within a period of less than 24 hours. The whole lip or eyelid may swell when wheals involve them. The itchy wheals are caused by release of histamine by mast cells in the skin. Treatment includes antihistamine medications.
When this process involves the tissues under the skin, a more diffuse and extensive swelling known as angioedema may occur. Occasionally, in a severe type of allergic reaction termed anaphylaxis, the swelling occurs in the throat causing airway obstruction. Anaphylaxis may also cause a sudden fall in blood pressure. This condition is a life-threatening emergency that requires immediate treatment with an injection of epinephrine and a rapid-acting antihistamine.
Short-lived attacks of urticaria and/or angioedema may be caused by allergy to a food or a medication, and in young children attacks may be provoked by infection. In some cases the problem may be provoked by physical factors such as cold, scratching, pressure on the skin or sweating. More rarely, exercise, heat, sunlight or mechanical vibration may provoke attacks. In the majority of cases of urticaria no cause can be found. Treatment for angioedema associated with urticaria is usually the same as the treatment for urticaria.
When the condition lasts for months it is the classified as chronic. In these patients and in patients with recurring short-lived episodes, causes that are external to the body are rarely found and routine allergy testing for foods and inhalants is not necessary. Approximately one half of patients with chronic urticaria have been found to have an antibody in the blood that attacks mast cells in the skin and causes them to release their histamine. Histamine, once released from mast cells, can make blood vessels leak fluid under the skin to cause swelling, and can stimulate pain-sensing nerves in the skin to cause itching. The treatment includes use of two types of antihistamines, and for severe episodes, corticosteroids taken orally.
Angioedema without a history of urticaria can be caused by certain drugs (ACE inhibitors), certain malignancies, and by an inherited enzyme deficiency (C1 esterase inhibitor deficiency). Symptoms of the hereditary enzyme deficiency problem typically include attacks of abdominal pain, vomiting, upper airway obstruction and non-itchy angioedema. This relatively rare disease requires treatment different from that of chronic urticaria and angioedema.
Atopic dermatitis, a type of eczema, is a different allergic skin condition in which affected skin is usually rough and inflamed, remaining unchanged in appearance over several days. Treatment of this condition is different from that of urticaria.
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