Hives — also known as urticaria (ur-tih-KAR-e-uh) - are raised, often itchy, red bumps (welts) on the surface of the skin; they can range in size from small spots to large blotches several inches in diameter. Acute hives can be an allergic reaction to food or medicine. They can also appear without cause. When you have an allergic reaction to a substance, your body releases histamine and other chemicals into the blood. This causes itching, swelling, and other symptoms. Hives are a common reaction. Persons with other allergies, such as hay fever, often get hives.
Angioedema is a related type of swelling that affects deeper layers in your skin, often around your eyes and lips. The most common treatment for hives and angioedema is antihistamine medication. In most cases hives and angioedema are harmless and don't leave any lasting marks, even without treatment but serious angioedema can be life-threatening if swelling causes your throat or tongue to block your airway.
Urticaria can usually be diagnosed by examining the distinctive red rash. You will also be asked questions to find out what triggered your symptoms. For example: when and where the rash began; what you had to eat just before it began and details of your usual diet; if you started taking any new medication just before your symptoms began. Allergy testing may be needed to find out if you're allergic to suspected triggers for urticaria. In around half of all cases of short-term (acute) urticaria, a cause can't be identified. If you have long-term (chronic) urticaria, a number of tests may be needed to identify the underlying cause. If your urticaria lasts for more than six weeks, it's very unlikely to be caused by an allergy, so allergy tests aren't usually recommended. You may be referred for a number of tests to find out if there's an underlying cause of your chronic urticaria. For example tests for anemia; thyroid function tests - which can be used to check for an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism); liver function tests - which can be used to check if you have any problems with your liver.
Your doctor may recommend over-the-counter antihistamines as a first step. If the uticaria persists your doctor may recommend prescription medication or combination of drugs such as histamine blockers or oral corticosteroids.
Researchers have identified many - but not all - of the factors that can cause hives. These include foods, insect bites, pollen and some plants, such as poison oak and poison ivy, and some medications. Some people develop hives just by touching certain items. Some illnesses also cause hives. Notify your physician immediately if you suspect that a specific medication is causing your hives.
Antihistamines - available either over the counter or by prescription - are a frequently recommended treatment for hives. They work by blocking the effect of histamine, a chemical in the skin that can cause allergy symptoms, including welts. Low-sedating or non-sedating antihistamines are preferred. They are effective and long-lasting (may be taken once a day) and have few side effects. Your allergist may recommend a combination of two or three antihistamines to treat your hives, along with cold compresses or anti-itch salves to ease the symptoms.
Severe episodes of urticaria may require temporary treatment with prednisone or similar corticosteroid medication. When hives are chronic and symptoms are not adequately controlled by antihistamines, an injectable medication (for example Omalizumab) or an oral immunosuppressant can be prescribed. These medications are effective at reducing the severity of the symptoms for many people.
If your reaction involves swelling of your tongue or lips, or you have trouble breathing, your allergist may prescribe an epinephrine (adrenaline) auto-injector for you to keep on hand at all times. These can be early symptoms of anaphylaxis, a potentially fatal allergic reaction that impairs breathing and can send the body into shock. The only treatment for anaphylaxis is epinephrine. If you develop hives and your injector is not nearby - or if using the auto-injector doesn't cause the symptoms to immediately improve - go to an emergency room immediately. You should also go to the emergency room after using an auto-injector.