Definition of Allergies

An allergy is an exaggerated or reaction to substances that are generally not harmful.

Causes, incidence, and risk factors

Allergies are relatively common. Both genetics and environmental factors play a role.


Allergy symptoms vary, but may include:

Signs and tests

The health care provider will perform a physical exam and ask questions such as when the allergy occurs.


Severe allergic reactions (anaphylaxis) require treatment with a medicine called epinephrine, which can be life saving when immediately given.

Expectations (prognosis)

Most allergies can be easily treated with medication.


Paula J. Busse, MD, Assistant Professor of Medicine, Division of Clinical Immunology, Mount Sinai School of Medicine, New York, NY. Review provided by VeriMed Healthcare Network. David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. – 6/29/2010

Allergic reactions
Allergy symptoms
Histamine is released
Introduction to allergy treatment
Hives (urticaria) on the arm
Hives (urticaria) on the chest
Hives (urticaria) - close-up
Hives (urticaria) on the trunk

ADAM Medical Encyclopedia

Article written by

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission ( URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability.