A sensitivity to a specific substance, called an allergen , that is contacted through the skin, inhaled into the lungs, swallowed, or injected.
Allergic reactions are fairly common.
They occur more often in people with a family history of allergies . Most reactions happen soon after contact with an allergen . Most of these reactions are mild and can be treated at home. While first-time exposure may only produce a mild reaction, repeated exposures may lead to more serious reactions. Allergic reactions vary.