A-Z Health Guide from WebMD: Symptoms
Allergic Reaction
Topic Overview
Allergies are an overreaction of the body's natural defense system
that helps fight infections (immune system). The immune system
normally protects the body from viruses and bacteria by producing
antibodies to fight them. In an
allergic reaction, the immune system starts fighting
substances that are usually harmless (such as
dust mites, pollen, or a medicine) as though these
substances were trying to attack the body. This overreaction can cause a rash,
itchy eyes, a runny nose, difficulty breathing, nausea, and diarrhea.
An allergic reaction may not occur the first time you are exposed
to an allergy-producing substance (allergen). For
example, the first time you are stung by a bee, you may have only pain and
redness from the sting. If you are stung again, you may have
hives or difficulty breathing. This is caused by the
response of the immune system.
Most people will have some problem with allergies or allergic
reactions at some point in their lives. Allergic reactions can range from mild
and annoying to sudden and life-threatening. Most allergic reactions are mild,
and home treatment can relieve many of the symptoms. An allergic reaction is
more serious when severe allergic reaction (anaphylaxis)
occurs, when
allergies cause other problems (such as nosebleeds,
ear problems, wheezing, or coughing), or when home treatment does not
help.
Allergies often occur along with other diseases, such as
asthma,
ear infections,
sinusitis, and
sleep apnea. For more information, see the topic
Allergic Rhinitis.
| Allergic Reaction: Topic Overview |
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Last updated: August 26, 2005
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This information is not intended to replace the advice of a doctor.
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