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allergic reaction

an allergic reaction is an overreaction of the immune system to a substance called an allergen. allergens include chemicals, foods, medicines, mould, plants, and pollen.

symptoms of an allergic reaction can range from mild and annoying to severe and life-threatening.

  • allergens can affect different tissues in the body, such as the airways, eyes, gastrointestinal tract, nose, lungs, and skin.
  • some allergic reactions, such as hives or itching around an insect bite or where a plant or chemical touched the skin, affect only one area of the body.
  • other allergic reactions may affect the whole body, causing itching all over, swelling, fainting, belly pain, nausea, vomiting, or difficulty breathing.
  • a severe allergic reaction (called anaphylaxis) can lead to shock and even death.

allergic reactions may not occur the first time a person is exposed to an allergen. a person may become more sensitive to the allergen with each exposure.

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this information does not replace the advice of a doctor. healthwise, incorporated, disclaims any warranty or liability for your use of this information. your use of this information means that you agree to the terms of use and privacy policy. to learn more about healthwise, visit healthwise.org. © 1995-2022 healthwise, incorporated. healthwise, healthwise for every health decision, and the healthwise logo are trademarks of healthwise, incorporated.

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