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A
Food allergy occurs when your immune system responds
defensively to a specific food protein that is not harmful
to the body.
The
first time you eat the offending food, your immune system
responds by creating specific disease-fighting antibodies
(called immunoglobulin E or IgE). When you eat the food
again, the IgE antibodies spring into action, releasing
large amounts of histamine in an effort to expel the
"foreign invader" from your body. Histamine
is a powerful chemical that can affect the respiratory
system, gastrointestinal tract, skin, or cardiovascular
system.
What
Are the Symptoms of a Food Allergy?
Symptoms
may appear almost immediately, or up to two hours after
you've eaten the food. Symptoms can include a tingling
sensation of the mouth, swelling of the tongue and throat,
hives, skin rashes, vomiting, abdominal cramps, difficulty
breathing, diarrhea, a drop in blood pressure, or even
a loss of consciousness. Severe reactions -- called
anaphylaxis -- can result in death.
Which
Foods Most Often Cause Allergic Reactions?
There
are six foods that cause 90% of food allergies in children
- milk, eggs, peanuts, wheat, soy, and tree nuts (such
as walnuts, pecans, and almonds).
In
adults, 90% of food allergies are caused by peanuts,
tree nuts, fish, and shellfish.
How
Are Food Allergies Diagnosed?
Your
doctor may do a radioallergosorbent blood test (RAST)
to check the number of antibodies produced by your immune
system. Elevated levels of certain types of antibodies
can help your doctor identify specific food allergies.
The
doctor may also perform an allergy skin test, also called
a scratch test, to identify the substances that are
causing your allergy symptoms.
Also,
by keeping a food diary, your doctor will have a much
better starting point to determine the foods that could
trigger your allergies. You may be asked to eliminate
all potentially allergenic foods and then add them back
to your diet one at a time to see if they prompt any
reaction. This is called an "elimination and challenge
diet".
How
Are Food Allergies Treated?
The
best way to cope with a food allergy is to strictly
avoid the foods that cause a reaction. Mild reactions
often will subside without treatment. For rashes, skin
creams may ease discomfort while antihistamines can
help reduce itching, congestion, and other symptoms.
For
more serious reactions, corticosteroids such as prednisone
will help to reduce swelling. In life-threatening situations,
an epinephrine injection can immediately begin to reverse
symptoms and is the only effective treatment option.
How
Can I Be Prepared?
Once
you and your doctor have determined which foods you
should avoid, stay away from them. However, it is important
that you maintain a healthy, nutritious diet. Ask your
doctor to recommend foods that will provide you with
the necessary nutrients.
You
should also be aware of the ingredients in processed
foods. Be sure to read labels. For instance, did you
know that vitamins, processed meats, and packaged dessert
mixes are often made with milk or dairy ingredients?
A registered dietitian can help you learn how to read
food labels to discover hidden sources of food allergens.
If
you are prone to allergic reactions, ask your doctor
to prescribe an epinephrine injection kit and carry
it with you at all times.
Reviewed
by the doctors at The Cleveland Clinic Department of
Pulmonary, Allergy and Critical Care Medicine.
Edited
by Charlotte E. Grayson, MD, Feb. 2004, WebMD.
Portions
of this page © The Cleveland Clinic 2000-2004
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