Inflammation (swelling) of the airways is the underlying cause of asthma
and there are two main reasons that people develop the disease, says Fernando Martinez, M.D., director of the Arizona Respiratory Center at the University of Arizona College of Medicine in Tucson.
"Asthma is caused in some people because they react to viral infections like the common cold. Another group is genetically predisposed to asthma, and for them, it is associated with the way the lungs grow and the way the immune system develops."
It is in this second group that asthma tends to be persistent, and there is often a family history of asthma and allergies. "Over the next decade," Martinez says, "determining which genes are involved in causing asthma will help scientists prevent and treat the disease."
William Busse, M.D., professor of medicine in allergy and immunology at the University of Wisconsin Medical School, says the causes of the increasing asthma rates are not fully understood.
He says that the prevalence of asthma is higher in developed countries, such as the United States, Europe, and New Zealand, and is lower in less developed areas, such as China and Africa. This suggests a possible role of environmental or lifestyle factors in the causes of asthma.
Researchers are exploring possible factors such as diet, frequent use of antibiotics, and fewer and less severe infections in early life. Busse says studies have shown that children who are enrolled in day care before 6 months of age have more frequent infections in early life, but significantly less asthma after age six.
Asthma also occurs more in urban environments than in farming ones. The Hygiene Hypothesis, first proposed in 1989, remains under debate and requires further study, according to Busse. This hypothesis states that environments that are too clean may actually make immune function more likely to develop allergic responses thereby possibly causing asthma.
In a study published in the Sept. 19, 2002, issue of The New England Journal of Medicine, researchers studied 812 children ages 6 to 13 living in rural areas of Germany, Austria, and Switzerland, and found that children in farming households experienced a decreased risk of hay fever and asthma.
