- An abnormal reaction of the body to a previously encountered allergen, which is typically harmless, such as pollen, certain foods, or certain medications.
- Sensitivity to a substance, typically a particular food or drug, that results in an overreaction of the immune system.
Early 20th century: from german allergie, from greek allos "other" + -ergos "working".
- He has a severe allergy to peanuts.
- She has an allergy to dust.
- He has an allergy to the medicine.
- She has an allergy to the pollen.
- He has an allergy to the cat hair.