An allergy is an inappropriate response by the body's immune system to a substance that is normally harmful. The immune system is a highly complex defense mechanism that helps us to fight infections. Allergic rhinitis/ hay fever is an inflammation inside the nose caused by an allergen such as pollen, foods like ( shellfish, milk, soya, strawberries, chocolate, peanuts, walnuts, and other tree nuts, fish, eggs and wheat) dust , molds, or flakes of skin from certain animals, animal hair, certain metals like nickel, some cosmetics, lanolin, dust mites, insect venom, some common drugs ( such as penicillin and aspirin) some food additives ( such as benzoic acid and sulfur dioxide), animal dander and the chemicals found in soap, washing powder, cleaning supplies, and many other chemicals.