Acute Care: Injuries and Illnesses
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.
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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
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.
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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.
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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
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.
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