Allergies are an abnormal response of the immune system to certain elements from outside the body. Some people react to a usually harmless substance called an allergen which can be dust, pollen, insect sting, food, cockroach and medicines. Allergies occur when the immune system misidentifies allergens, and reacts to them as if they were harmful. Some reactions, called allergy symptoms, can be similar to some illnesses. See a health worker to have a correct diagnosis.
Attribution: Straight Talk Foundation