Environmental Factors - What Causes Asthma: Asthma
Content provided by the Faculty of the Harvard Medical School
Environmental factors
It is likely that inhaled substances are the most important environmental factors contributing to the development of asthma in people with a genetic predisposition to the disorder. The leading suspects are allergens (substances that cause an allergic reaction; see "The allergy connection"). Other potential culprits include tobacco smoke, air pollution, and infectious agents such as viruses and mycoplasma. Asthma most often develops during childhood following exposure to one or more of these environmental factors, but it can also develop in adulthood.
Adults who smoke, who are exposed to irritating chemicals in the workplace, or who suffer a particularly nasty respiratory infection may develop asthma. A number of specific occupations can expose workers to agents that can trigger asthma (see "Selected causes of occupational asthma"). Hormone replacement therapy in menopausal women is another risk factor: The Nurses' Health Study, a large epidemiological study that has collected information about women's health issues since 1976, found that menopausal women who were currently using or who had used estrogen replacement therapy had a 50% greater risk of developing asthma than those who did not take hormones. In addition, a study of more than 2,000 women found that hormone replacement therapy may increase women's risk of asthma and wheezing, particularly if they are lean. Often, however, there is no identifiable cause of adult-onset asthma. In some cases, the problem may have been present in childhood but was undiagnosed, or it may have been present in childhood, become dormant around adolescence, then resurfaced in adulthood.
The same environmental factors that are thought to incite asthmatic inflammation of the bronchial tubes in the first place can also cause subsequent asthma attacks. Learning to recognize and avoid your asthma triggers is an important part of managing the disorder (see "Asthma triggers").
Selected causes of occupational asthma | |
| Agents | Occupation |
| Animals | Animal handlers Laboratory workers Veterinarians |
| Plants | Grain handlers Bakers Natural oil manufacturing workers Tobacco and food processing workers Health care workers |
| Enzymes | Bakers Detergent, pharmaceutical, and plastic industry workers |
| Vegetable products | Printers Gum manufacturing workers |
| Some shellfish | Crab, shrimp, and prawn processors |
| Diisocyanates | Polyurethane industry workers Plastics workers Workers using varnish Foundry workers |
| Anhydrides | Epoxy resin and plastics workers |
| Wood dust | Carpenters Sawmill workers Furniture makers |
| Metals | Platinum- and nickel-refining workers Hard-metal workers |
| Soldering fluxes | Solderers |
| Drugs | Pharmaceutical and health care industry workers |
| Other organic chemicals | Chemical, plastic, and rubber industry workers Hospital workers Laboratory workers Foam insulation manufacturing workers Food wrapping workers Spray painters |
| Last updated: | September 27, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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