Your health care provider will examine you and ask questions about how the hives or angioedema started. Tell him or her about the following. Any medicines (prescription and nonprescription) you have been taking even if you stopped them in the past few days. Any dietary supplement or herbs you take, even if only sometimes, and the last time you took them.

Any new or unusual foods, soaps, detergents, and cosmetics. Any allergies that you know about. Any recent illnesses you have had such as sore throat, cough, runny nose, vomiting, or diarrhea. Any chronic illnesses such as diabetes, liver disease, or kidney disease. If there is the possibility you are pregnant.

If your health care provider cannot tell what triggered your hives or angioedema, he or she may recommend that you see an allergy specialist (allergist). Even using special skin tests, however, it may not be possible to identify the trigger.

Stop any food or medicine identified as the cause of the hives or angioedema. In very mild cases, no treatment at all may be required. If symptoms are making you uncomfortable, take a nonprescription antihistamine, such as diphenhydramine (Benadryl), by mouth, per the package instructions or as directed by your health care provider, until symptoms subside. These can be effective for mild episodes. Antihistamines may make you too drowsy to drive or operate machinery safely.

Cool compresses or baths may help with the discomfort. Avoid hot baths or showers. Avoid direct sunlight. Wear light, loose-fitting clothing. Avoid strenuous activity or anything that might cause sweating. Try to relax and reduce stress.

Severe reactions do not attempt to treat severe reactions or to wait it out at home. Go immediately to the nearest emergency department or call an ambulance. Here are some things you can do while waiting for the ambulance:

Try to stay calm. If you can identify the cause of the reaction, prevent further exposure. Take an antihistamine, such as 1-2 tablets or capsules of diphenhydramine (Benadryl), if you can swallow without difficulty. The liquid form of diphenhydramine (Benadryl) can also be used at 2-4 teaspoons (10-20 mL) per dose.

If you are wheezing or having difficulty breathing, use an inhaled bronchodilator, such as albuterol (Proventil), if one is available. These inhaled medications dilate the airway.

If you are feeling light-headed or faint, lie down and raise your legs higher than your head to help blood flow to your brain. If you have been given an epinephrine kit, inject yourself as you have been instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms.

Bystanders should administer CPR to a person who becomes unconscious and stops breathing or does not have a pulse. If at all possible, you or your companion should be prepared to tell medical personnel what medications you take and your allergy history.

The treatment of hives depends on the severity of the symptoms. For mild to moderately severe localized symptoms, a nonprescription antihistamine by mouth is usually adequate, along with skin care measures for comfort. For more severe cases, an injection or short course of a corticosteroid may be needed to rapidly reduce swelling and itching.