Antibodies are substances produced in response to bacteria, viruses and allergens. These antibodies counteract or destroy bacteria and viruses. In allergic individuals, however, when these allergy-related antibodies react with the allergens, special cells known as mast cells are activated. This reaction causes irritation and swelling in sensitive areas of the body, such as the nose, eyes, lungs, skin and digestive system. Initially, a person may not be sensitive to an allergen, but may develop sensitivity after repeated exposure, sometimes after years of exposure.
Hay fever can be a seasonal or year-round health problem.
The muscles around the airways can contract, causing the airways to narrow even more. When the lining of the airways is inflamed, it produces mucus that clogs the airways and further blocks the flow of air. Because of the insidious nature of this condition and the special care required, asthma is discussed further in a separate section in this guide. If not treated early, atopic dermatitis can be complicated by a secondary infection. Contact dermatitis is a rash that is caused by direct skin contact with certain substances.