Allergy is a condition that occurs when an individual's immune system is hypersensitive or over-reactive. Ordinarily, the human immune system has a fine-tuned ability to distinguish between harmless substances in the environment, such as dust, and potentially harmful agents, such as viruses and bacteria. For an individual with allergies, however, the immune system reacts quickly, intensely, and inappropriately to one or more foreign substances that are ordinarily harmless.
The foreign substance that triggers an allergic reaction is called an allergen or antigen. When individuals with an allergy eat, touch, or inhale the particular foreign substance or allergen, their immune system mistakenly launches an attack against it. Allergic individuals produce an antibody called immunoglobulin G (IgG) as well as a large amount of another antibody called immunoglobulin E (IgE). IgE is responsible for generating a full-scale reaction with symptoms such as swelling, skin rashes, or constant sneezing or coughing each and every time the individual is exposed to the offending substance (allergen).
In addition to heredity or genetic traits, certain environmental exposures (e.g., tobacco smoke), emotional factors, and conditions of physiological stress (e.g., puberty, pregnancy, or illness) may predispose individuals to allergic symptoms. Food, drugs, mold, pollen, insect bites, infection, physical agents (e.g., heat, cold, sun, pressure, or exercise), polyurethane plastics, paints, varnish, and latex or rubber products may trigger allergic reactions. Recently, there have been growing reports of allergic reactions to water-soluble proteins in latex products (e.g., rubber gloves, dental dams, condoms, and medical devices), particularly among medical personnel and individuals receiving medical care. Animal dander is another common occupational allergen that typically affects farmers, veterinarians, groomers, and laboratory workers. Hospital workers, photographers, and food service workers most commonly encounter allergenic chemicals such as formalin, hexachlorophene, ethylene diamine, and metabisulfite. Dust from flour, grains and wood can affect mill workers, carpenters, bakers, and lumberjacks.
Allergic reactions are usually relatively localized to one or more body systems. For example, hay fever (allergic rhinitis) causes a runny nose and sneezing, allergic conjunctivitis is characterized by itching and red eyes, and bronchial asthma causes narrowing of airways. Ocular (or eye) allergies result in symptoms of itching, redness, and tearing of the eyes following exposure to allergens in the air or substances coming in contact with the eye. Allergic conjunctivitis is the most common ocular allergy and occurs in the spring and fall months in conjunction with hay fever.
On rare occasions, an allergic reaction can result in a whole body response (anaphylaxis). This sudden, life-threatening allergic reaction can trigger a swollen throat and a constriction of the airways, rapid pulse, loss of consciousness, and a sudden drop in blood pressure (shock).Incidence and Prevalence: Approximately 50 million Americans have one or more significant allergies and suffers from a wide array of symptoms, and the incidence is increasing. Each year, Americans lose 3.5 million workdays because of allergies. Allergic rhinitis, often referred to as hay fever, affects more than 35 million people. This reaction to outdoor airborne allergens, usually tree and grass pollen, occurs on a seasonal basis. A second type of airborne allergy called perennial allergic rhinitis occurs year-round and is more likely due to indoor allergens such as pet dander or dust mites. Approximately 6 to 10 million Americans are allergic to animal dander and about 2 million have allergic reactions to insect stings. Food allergies occur in about 8% of children but affect only 2% of adults. Approximately 17 million Americans have asthma caused by allergies, 5 million of whom are children ("Tips to Remember"). |