For hives or localized skin reactions, perform the following:

• Take cool showers or apply cool compresses.

• Wear light clothing that doesn’t irritate your skin.

• Take it easy. Keep your activity level low.

• To relieve the itching, apply calamine lotion or take nonprescription antihistamines, such as diphenhydramine (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton).

For more severe reactions, self-treatment is not recommended. Call your health-care provider or 911, depending on the severity of your symptoms. If you have symptoms of anaphylaxis, here’s what 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 (one to two tablets or capsules of diphenhydramine [Benadryl]) if you can swallow without difficulty.

• If you are wheezing or having difficulty breathing, use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) 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 any known allergies.