Acute Urticaria
Hives lasting less than six weeks are caused by "acute urticaria".
With this type of hives, the cause can usually be found. The most
common causes are foods, drugs or infections. Insect bites and
internal disease may also be responsible. Other causes can be
pressure, cold, and sunlight.
Foods
The most common foods that cause hives are nuts, chocolate,
fish, tomatoes, eggs, fresh berries and milk. Fresh foods cause
hives more often than cooked foods. Food additives and preservatives
may also be the problem.
Hives may appear within minutes or up to two hours after eating,
depending on where the food is absorbed in the digestive tract.
Drugs
Almost any prescription or over-the-counter medication can cause
hives. Some of those drugs include antibiotics, pain 
medications,
sedatives, tranquilizers, and diuretics. Antacids, vitamins, eye
and ear drops, laxatives, vaginal douches, or any other non-prescription
item can be a potential cause of hives. If you have an attack
of hives, it's important to tell your doctor about all of the
preparations that you use to assist in finding the cause.
Infections
Many infections can cause hives. Colds are a common cause in
children.
Chronic Urticaria
Hives lasting more than six weeks are called "chronic urticaria".
The cause of this type of hives is usually much more difficult
to
identify than that of acute urticaria. In patients with chronic
urticaria, the cause is found in only a small number of patients.
Your doctor will need to ask many questions in an attempt to find
the possible cause. Since there are no specific tests for hives,
testing will depend on your medical history and a thorough examination
by your dermatologist. Routine blood tests are of little or no
value.
Physical Urticarias
Hives can be caused by sunlight, cold, pressure, vibration,
or exercise. Hives due to sunlight are called solar urticaria.
This is a rare disorder in which hives from within minutes of
sun exposure on exposed areas and fade within one to two hours.
Hives due to the cold are more common. These appear when the skin
is warmed after exposure to cold. If the cold is over large areas
of the body, large amounts of histamine may be released which
can produce wheezing, flushing, generalized hives, and fainting.
A simple test for this type of hives can be done by applying an
ice cube to the skin.
These hives can form after firmly stroking or scratching the
skin "dermatographism". It affects about 5 percent of
the population. Most people with this condition are otherwise
healthy. These hives can also occur along with other forms of
urticaria. If it is present along with hives, finding and eliminating
the cause usually clears the dermatographism. Otherwise, it may
last for months or even years.
Treatment
The best treatment for hives is to find and remove the cause.
This is not an easy task. Antihistamines are usually prescribed
by your dermatologist to provide relief. Antihistamines work best
if taken on a regular schedule to prevent hives from forming.
No one antihistamine works best for everyone, so your dermatologist
may need to try more than one or different combinations to find
what works best for you.
In severe hives, an injection of epinephrine (adrenalin) or a
cortisone medication may be needed.
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