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Hives are usually the result of "immediate" or "anaphylactic" allergy. They occur within several minutes to about 8 hours after exposure to an allergen (the substance you are allergic to).

What are Hives?

Hives are usually the result of an allergic reaction. This reaction causes release of histamine from cells in the skin. Histamine causes the blood vessels to dilate and leak fluid into the surrounding tissue causing the skin to swell. This reaction irritates nerve endings resulting in itching. In severe reactions, feeling of nausea, vomiting and dizziness may be present. The medical name for hives is urticaria. Hives are usually the result of "immediate" or "anaphylactic" allergy. They occur within several minutes to about 8 hours after exposure to an allergen (the substance you are allergic to). Any individual hive will last only a few hours and then fade, but new ones will occur.

Hives can occur anywhere on the body, but are especially common about the elbows and knees. They are usually small, ranging from 1 to 3 cm. in size. However, giant hives can occur covering large areas, most commonly on the trunk. Release of histamine will sometimes cause swelling of the eyelids, lips and tongue. Hives are usually not dangerous, but swelling of the lips can be alarming, and may indicate a more severe allergic reaction. If the tongue swells or any difficulty in breathing occurs immediate medical attention should be sought.


Many times it is very difficult to discover what allergen is inducing them hives. Most frequently, the allergen is something ingested such as food or medicine; or inhaled, such as fumes from chemicals, pollen, animal danders, etc. However, it can also be something applied to mucous rectum. Injections are another common entry mechanism for allergens. The least common trigger is something applied externally to the skin.

Another possible source of the allergen is from within the body, very commonly an infection. Thus it is possible to get hives from a viral infection (including colds, flu, hepatitis, mono, and herpes) and bacterial infections such as urinary tract infections. Internal parasitic infestations also may induce hives.

Sometimes hives are triggered by nervous tension and stress. Other less common inducers of hives are reactions to cold, heat, sunlight, water and physical exertion. In these cases, histamine is released by a nonallergic mechanism, but the hives are the same in appearance and symptoms.

Many times the inducer of the hives is never discovered. The hives may last for 4 or 5 days and then disappear, leaving you perplexed but healthy. If the hives persist for more than a week, it is a good idea to seek medical advice and evaluation.


Hives are best treated by removing the inducer. All drugs not critically important to health, including aspirin and vitamins, should be stopped, even if you have taken them safely for years. If you are taking an important drug such as for seizure control or for a heart condition, consult your physician before discontinuing it. In order to become allergic to a drug, you must first be exposed to it, so the inducer of your allergy may be something that you've taken before without problems. Foods are more difficult to incriminate; however, examine the time association of the hives to ingestion of certain foods. Usually hives will appear within 8 hours of eating something and will then disappear and not reappear unless the same food is eaten again.

What can you do?

A daily diary may be helpful in discovering the inducer of hives. Make 4 columns on a sheet of paper. In the first column put in the time of day, in the second column list all foods eaten, in the third column record your activities and location, and in the fourth column record onset of hives. Column 3 is important because the inducer of your hives may be related to a specific activity or it may be in one location you visit which may give you a vital clue. Also record exposure to animals and birds. After several days, look at your diary and see if any correlations exist.

Specific suppressive treatment for hives is to take an antihistamine. This will counteract the histamine your body is releasing. It will not cure the underlying condition which is inducing the hives. You can buy an antihistamine tablet called chlorpheniramine (4 mg) without a prescription and take 1 or 2 tablets every 4 hours as needed. The main side effect of the antihistamine is drowsiness, so do not plan to operate machinery, drive a car or ride a bike at least until after you know how much it affects you. Some people prefer to itch a bit from the hives than to suffer the drowsiness often caused by the treatment. If your hives occur at night, the antihistamine will usually ensure a good night's sleep without itching, if taken at bedtime. It is best to take the antihistamine at least 20 minutes before bedtime so that it will be starting to act at bedtime.

Hives can also be treated by applying cold wet compresses or ice packs. Cold usually reduces swelling and relieves itching. Hot showers, being dressed too warmly, alcohol, and physical exercise usually make hives worse. Do not take aspirin as it may make hives worse. Creams or lotions applied to the skin do not help hives.