Symptoms and Signs of Allergic Reaction

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Medically Reviewed on 4/8/2019

Doctor's Notes on Allergic Reaction

An allergic reaction is an exaggerated response by the body's immune system to a substance in the environment. Allergies are caused by an inappropriate or misguided reaction to foreign substances. The substances that trigger allergic reactions are called allergens. There are many different kinds of allergens, including pollens, plants, eggs, nuts, foods, and animal dander.

Signs and symptoms of an allergic reaction include itching and watering of the eyes, nasal congestion, sneezing, runny nose, scratchy throat, and cough due to postnasal drip. Other associated symptoms can include fatigue, lethargy, hives, rash, and itching of the skin. Anaphylactic reactions are serious allergic reactions that can be life-threatening. In an anaphylactic reaction, swelling of the throat leads to difficulty breathing.

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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.