seventeenth-century Belgian physician and asthmatic named Jean Baptista van Helmont called asthma the "falling sickness of the lungs." I know what he meant. As an allergic asthmatic, I am hypersensitive to substances that may have no effect at all on someone standing next to me. All it takes is a speck, a drop, a few molecules, and my immune system responds as if I were being attacked by something virulent. T cells, macrophages, eosinophils, and other immune system cells flood into the tissues of my airways, setting off an immunological train wreck. As my airways become inflamed and swollen and start producing mucus, I cough, drip, and wheeze. The immune system cells also prompt the most frightening response -- constriction of the smooth muscle of my bronchial tubes. This is van Helmont's "falling" effect. It feels as if my airways were collapsing.
What makes the asthmatic's airways so hypersensitive? Genetics plays a part; I probably inherited my asthma from my asthmatic father. But DNA isn't the whole story. "Genetic changes haven't occurred rapidly enough to account for the global increase in asthma," says Anne Wright of the Arizona Respiratory Center at the University of Arizona in Tucson. "It pretty clearly has something to do with our interaction with the environment."
One theory suggests that modern society may be too antiseptic for our bodies. Over the last hundred years, humans' relationship to microorganisms has changed dramatically. When people were born in homes, didn't bathe as regularly, and didn't use antibiotics, they encountered more germs. Children got more sick more often. But exposure to microbes may have forced children's immune systems into maturity -- and strengthened them against exposure to allergens. In one study following 1,200 people for more than two decades, Wright and her colleagues found that those who attended day care as children, or whose family owned a dog when they were growing up, tended to have less asthma than others. What do dogs and day care have in common? Bacteria -- mostly from feces, Wright explains. "We all know poop's not good for you," she says. "You can get sick from it. But what also happens is that your immune system is developing antibodies and being activated by those organisms."
Although Wright subscribes to the hygiene hypothesis, she and other researchers agree that asthma, like cancer, has no single cause. "We won't find treatments and cures and preventive measures if we don't address the disease from different points of view -- environmental, genetic, molecular, biological," says Fernando Martinez, director of the Arizona Respiratory Center. Children and adults who have been frequently exposed to tobacco smoke and to indoor allergens from cats, cockroaches, and household dust mites have more asthma than those who haven't. The disease is more prevalent and more severe among poor people. It's more common in inner cities. Stress may cause asthma. Sedentary lifestyles and unhealthy diets have also been associated with asthma.
o wonder asthma has seemed exhaustingly complicated all my life. Even the suggested remedies are overwhelming -- everything from smoking marijuana to giving up dairy products to inhaling steroids to refraining from sex. And the mystery of asthma's causes has always left me asking, "Why me?" Why does standing near a horse throw my lungs into a wheezing fit, and not the next guy's?
On pollution, scientists are making progress. Several long-term, multimillion-dollar studies are now underway to track children from the womb onward, measuring precisely what contaminants they're exposed to and recording who develops asthma and who doesn't. One study will investigate effects of the mix of air pollutants and pesticides that descends on children in central California. In the next few years, this research should start to shape concrete answers.
And last February, researchers from the University of Southern California published the most persuasive evidence yet linking asthma and air pollution. The study followed more than 3,500 children from twelve Southern California communities, six of which endured the kind of smog for which the Los Angeles region is notorious, and six of which had fairly clean air. Smog's primary ingredient is ozone, a caustic gas formed when sunlight and heat acts on certain air pollutants -- namely, nitrogen oxides and hydrocarbons. In Southern California, by far the largest source of these pollutants is tailpipes.
None of the children had asthma when the study began. After five years, 265 were diagnosed with it. But the critical finding was that children who lived in high-ozone areas and were involved in several team sports were three times more likely to develop asthma than couch potatoes living in less polluted communities. "Kids playing three or more sports are likely to be outdoors ventilating at high rates, and are therefore being exposed to higher levels of air pollution," explains James Gauderman, one of the study's authors.
But it's only a beginning. Martinez is one researcher who says the findings are important but not conclusive. High rates of asthma in cities may be related to factors such as stress, he argues. And he points out that asthma comes in different varieties. In the days when East Germany was highly polluted, its population had higher rates of asthma -- but fewer allergies -- than West Germans. It's possible, Martinez says, that pollution is not a risk factor for the allergic form of the disease, but may be a factor for another form of the disease.