An Epidemic No One Understands

Both had eczema, too, and the kind of food allergies — to nuts, peanuts and shellfish — that can lead to fatal reactions.

What caused all this? My husband and I were mystified, because neither of us had asthma or life-threatening allergies, nor did our parents or siblings. I do have hay fever and allergies to cats and dogs, but I had always considered my symptoms just a nuisance — not a bad omen for the next generation. My husband isn’t allergic to anything.

But we seem to have been caught on a rising tide that no one fully understands. Our sons were born in 1984 and 1987, and we encountered an awful lot of children their ages who had the same illnesses, far more than we remembered from our own generation.

Statistics suggest that something strange was occurring in those years. From 1980 to 2003, the prevalence of asthma in children rose to 5.8 percent from 3.6 percent, an increase of about 60 percent, according to the Centers for Disease Control and Prevention.

Other estimates from the disease centers show an even bigger increase in the asthmas rates for younger children: a 160 percent jump in those younger than 5 from 1980 to 1994. But changes in data collection starting in 1997 make it hard to compare the figures before and after that year. More recently, the rates seem to have leveled off in the United States and in other Western countries. In any case, about 20 million people in the United States have asthma today, including at least 6 million children, and 5,000 people a year die from it. Children in the inner cities seem to be especially hard hit, with exposure to cockroaches and diesel fumes suspected as the culprits. But the cause is not known for sure.

Worldwide, the disease has also increased. From 1985 to 2001, the prevalence rose 100 percent. About 300 million people have asthma, 255,000 die from it, and deaths could increase by 20 percent over the next 10 years, according to the World Health Organization. The problem is especially severe in developing countries, which are least able to provide the long-term intensive treatment that asthma requires.

Some of the apparent increases may not be real, but may have occurred because doctors got better at making the diagnosis. But increased reporting seems unlikely to account for all the new cases.

Theories come and go, and when you come right down to it, no one really knows why some people develop asthma and others don’t.

In “The Asthma Epidemic,” an article published last week in The New England Journal of Medicine, doctors tried to sort out various theories about the causes of asthma and explain why rates have risen. But there are no clear-cut answers.

Like other chronic diseases, asthma is probably caused by multiple genes and environmental exposures, and it can have quite different causes in different people. About half the cases are thought to stem from allergies and the rest from other problems that can irritate and inflame the airways, causing them to close.

Genetic changes in the population cannot explain the increasing rates, though, because such changes occur too slowly to account for the rapid increases in asthma, the authors said, suggesting that environmental factors are more likely candidates. But what has changed enough in the environment to explain spiking asthma rates?

The authors of the article, from University Children’s Hospital in Munich, review many study findings. They report that one clear risk factor is secondhand tobacco smoke. Exposure to it does increase asthma risk in infants and small children. But how would that explain the increases, when over all, parents today smoke less than previous generations?

People frequently blame air pollution for causing asthma, but its role is not entirely clear. Pollution does makes asthma worse in people who already have the disease, but it’s not known whether pollution also makes asthma develop in the first place. And in any case, air pollution in the United States has decreased in the last few decades. Living in a place with high vehicle exhaust may make asthma worse, but the evidence is “relatively weak,” the researchers report.

Dust mites, microscopic insects that live in bedding and furniture, were long blamed for causing asthma to develop in infants and small children and have led to a booming industry of mattress covers, air filters and guilt-ridden parents tethered to dust mops and vacuum cleaners. But recent studies have questioned the connection. Once children have asthma, though, the mites and their droppings may make the symptoms worse.

Cat dander has become a complete puzzle, with some studies finding that exposure early in life leads to asthma, and others saying it protects against asthma. At this point, nobody knows which study to believe, but most experts agree that when people already have asthma, being around cats can make it worse.

Under some of the theories, I should have had the world’s worst asthma. Clearly, I had allergic tendencies, and the experts would have shuddered at my environment. I grew up in New York in a small apartment with parents who were heavy smokers, on a busy street with trucks rumbling by and a bus stop in front of the door. Buildings all around us burned coal. At times, we had a dog, a cat, parakeets and, briefly, a duck. It’s amazing that the pets survived the smoke. My mother was a decent housekeeper, but she wouldn’t have won any prizes. I never wheezed. Go figure.

Obesity and asthma have also been linked in some studies, but the link, if it exists, is not understood. Researchers say it is simply not a matter of asthmatic children growing fat because they cannot exercise. The weight gain can be first.

Nutrition is another mystery. Studies of fruits, vegetables, cereals, fatty acids, vitamins, minerals and antioxidants have been inconclusive, and little is known about the effects from what pregnant women eat. Experiments in which pregnant women avoided cow’s milk and eggs in hopes of preventing asthma in their infants did not work, and breast-feeding doesn’t prevent the disease, either.

One theory that has received attention recently is the “hygiene hypothesis,” the idea that children today are raised in homes that are too clean and that asthma is somehow caused by the lack of exposure to infections and bits of microbes early in life. Under this theory, germs are supposed to help the immune system develop normally, and without them the system may overreact to other substances in the environment, producing allergies and asthma.

There is some evidence to support the idea. Studies find that children raised on farms are less prone than others to asthma, maybe because they are exposed to plenty of microbes in barns and stables. But the connection is still not fully understood, and some viral infections clearly make asthma worse.

A related idea is that the increased use of antibiotics in recent decades contributes to asthma by changing the type of the bacteria that live in the gut. But that has not been proved. Some researchers have suggested that acetaminophen, used to treat pain and fever, may be linked to asthma. Its use increased in the 1980s, after pediatricians declared aspirin unsafe for children. But that theory has not been proved, either.

Ultimately, this new list of the usual suspects still doesn’t solve the mystery.

Gradually, my sons’ asthma diminished. Both became track and cross-country runners in high school, and now, as they have gone on to college and graduate school, the disease is rarely a problem. But it was a worry that hung over us for a long time.

As for the food allergies, we choose to assume that they last for life. The only way to find out for sure is called a “challenge,” in which you eat the risky food with doctors standing by to revive you in case it turns out that, gee, you’re still allergic to it after all. Somehow, I don’t think we’ll be signing up for that.

My sons have adrenaline kits to treat a severe reaction. Neither has ever needed it, and I know they don’t carry it around the way they’re supposed to when they go to restaurants.

Needless to say, I wish none of this had ever happened. But, based on what’s now known, could I have done anything to prevent it? Was it bad that we had cats when our children were born or that we later gave them away? Asthma transformed me and my husband from rather casual housekeepers into mop-wielding fanatics. I’m not sure it helped.

Suppose I had recognized that my own allergies meant that my children would be at risk. Would it have helped if I had then avoided eating nuts, peanuts and shellfish while I was pregnant and breast-feeding? I don’t think the answer is clear.

Similarly, I’m not convinced that it would have made a difference if I had been more cautious and methodical about introducing new foods in their first few years, though allergy groups recommend it. The only thing that seemed to do them any good was asthma medicine, and lots of it.

Because children who have even one parent with allergies and asthma have an increased risk of developing the same problems, it would be great if somebody could figure out a way to lower that risk in time to help my sons and the millions of other young people who were also caught in the asthma wave, when they decide to become parents. I am hoping, but I know it may be a problem with many solutions — or none.