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Which substances commonly trigger allergic reactions?

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immune system disorder False-color scanning electron micrograph of a T cell infected with HIV (human immunodeficiency virus), the agent that causes AIDS (acquired immunodeficiency syndrome).

Allergic reactions occur when the immune system overreacts to typically harmless substances known as allergens. These substances can be inhaled, touched, or ingested, triggering a range of responses from mild irritation to severe, life-threatening conditions like anaphylaxis.12

Common triggers include:

Foods: Proteins found in cow’s milk, eggs, peanuts, tree nuts, wheat, soy, fish, and shellfish.12
Environmental factors: Pollen, dust, and dust mites.12
Animals: Pet dander (skin flakes) from cats and dogs.1
Medications: Various drugs, including penicillin, aspirin, ibuprofen, tetracyclines, and digitalis.3
Insects: Venom from bees and wasps.42
Other: Molds and various chemicals.1

When a sensitized individual is reexposed to these allergens, the body releases substances such as histamine, which leads to symptoms like tissue swelling, sneezing, wheezing, and skin reactions such as hives.142