(allergy) An allergy is a reaction by your immune system to something that does not bother most other people. People who have allergies often are sensitive to more than one thing. Substances that often cause reactions are Pollen; Dust mites; Mold spores; Pet dander; Food; Insect stings; Medicines. Normally, your immune system fights germs. It is your body's defense system. In most allergic reactions, however, it is responding to a false alarm. Genes and the environment probably both play a role. Allergies can cause a variety of symptoms such as a runny nose, sneezing, itching, rashes, swelling, or asthma. Allergies can range from minor to severe. Anaphylaxis is a severe reaction that can be life-threatening. Doctors use skin and blood tests to diagnose allergies. Treatments include medicines, allergy shots, and avoiding the substances that cause the reactions.

(allergy) An allergy is an immune response or reaction to substances that are usually not harmful.

(allergy) An immune system reaction (for example, rash, fever, sneezing, or headaches) to something that is normally harmless.

(allergy) Hypersensitivity to an agent caused by an immunologic response to an initial exposure

Altered reactivity to an antigen, which can result in pathologic reactions upon subsequent exposure to that particular antigen.

An exaggerated response by the immune system to a drug or other substance.

An immune response that occurs following exposure to an innocuous antigen, but that does not require the presence of preformed antibodies to the antigen.

An inflammatory response to an exogenous environmental antigen or an endogenous antigen initiated by the adaptive immune system.

State of previously immunized body in which tissue damage results from the immune response to a further dose of antigen.

(hypersensitivity reaction) An excessive immune system response to a substance that is not usually considered harmful.

(hypersensitivity/allergic reaction) A local or general reaction of an organism following contact with a specific allergen to which it has been previously exposed and to which it has become sensitized.

Allergies occur when your immune system reacts to a foreign substance - such as pollen, bee venom or pet dander - or a food that doesn't cause a reaction in most people.

Allergy, hypersensitivity reaction by the body to foreign substances (antigens) that in similar amounts and circumstances are harmless within the bodies of other people. Antigens that provoke an allergic reaction are called allergens. Typical allergens include pollens, drugs, lints, bacteria...