Emily Ferraro, 11, of Adams, loves to play soccer. She plays for two teams, the Mars Area Soccer Club and Northern Crew.

Emily is active despite suffering from asthma, which apparently was brought on by the vigorous exercise she gets playing soccer.

Asthma is a chronic disease that affects the airways, the tubes that carry air in and out of the lungs.

In asthmatics, these airways are very sensitive. They become swollen when irritated. As they swell, the airways become narrower, and less air flows to the lungs. Sometimes cells produce more mucus than usual, which clogs the airways further.

The symptoms of asthma are wheezing, coughing, chest tightness, and trouble breathing, especially at night and early in the morning.

Asthma is the most common chronic condition among children in North America, affecting about one in 15. About one adult in 20 also is afflicted.

Rates among athletes for exercise-induced asthma are much higher. A recent study at Ohio State University of 107 varsity athletes found that 42 tested positive for asthma. Of these, 36 had no prior history of asthma.

The problem may be more widespread than the Ohio State study indicates, said Dr. Moira Davenport, a sports medicine physician with Allegheny General Hospital.

"A very high percentage of highly competitive athletes -- perhaps as many as 70 percent -- suffer from this," Dr. Davenport said.

Dr. Davenport, 35, has firsthand knowledge. She developed exercise-induced asthma while running track and cross country in high school in New Hampshire.

"I've never had a typical asthma attack," she said. "It's always been after exercise."

Asthma is incurable, but is relatively easy to control if diagnosed and treated early.

"It's not a difficult problem to treat," said Dr. Deborah Gentile, director of research for the division of asthma, allergy and immunology at Allegheny General Hospital. "It's more a matter of raising awareness that it's out there. Over 95 percent of our patients we can control very well so that they can do the activities they want."

Dr. Davenport, her AGH colleague, can attest to that. She's run the New York City marathon four times since she was diagnosed with exercise-induced asthma.

An indication of how effective asthma treatments have become is that some athletes who don't have exercise-induced asthma are claiming to be suffering from it, so they'll be able to take the medications as performance enhancers, Dr. Davenport said.

Emily Ferraro said she has an inhaler, which she is supposed to use every morning. Inhalers typically contain beta agonists such as albuterol and pirbuterol, which help to dilate the muscles along the airways to permit more air to enter the lungs.

"Sometimes if I forget to use it, when we are running laps before practice starts, my mouth gets really dry and I have trouble breathing," she said. "So I have to stop and get my inhaler."

Quinn Hood, 15, a sophomore fullback for Baldwin High School, was diagnosed with exercise-induced asthma after he had trouble breathing during a basketball game when he was in the fourth grade.

"I use an inhaler before practice, and I'm fine afterwards," he said.

Treatments for asthma have gotten so good that asthmatics who until recently would have been discouraged from vigorous physical activity are now being encouraged to exercise.

"Twenty years ago, if you had asthma, you weren't supposed to participate in sports," said Dr. Tanya Hagen, a sports medicine physician at UPMC and the head team physician for Robert Morris University. "Now people are saying that exercise is so important from a health standpoint that we're going to promote exercise even in that population."

But if left untreated, asthma can have serious consequences. About 5,000 deaths in the United States each year are attributed to asthma.

Asthma, which was first diagnosed by Hippocrates, the father of medicine, in 450 B.C., is one of the oldest medical conditions known to man. (The word "asthma" comes from the Greek word "aazein," which means "sharp breath.")

Physicians think the recent rise in the prevalence of asthma is related to rising levels of pollution, but why some people get asthma and others don't is still something of a mystery.

"Is it a population of children of smokers? Is it something in the environment? More research needs to be done," Dr. Hagen said.

The athletes most likely to suffer from exercise-induced asthma are those who play winter sports such as skiing or ice hockey.

"The cold, dry air they breathe is the opposite of what we have in our lungs," Dr. Davenport said. "The sheer volume of that air that people take in can shock the system."

Another contributor to exercise-induced asthma, Dr. Gentile said, is that people who are engaged in vigorous exercise tend to breathe more through their mouths than through their noses. The nose warms and filters air in ways the mouth doesn't.

People with allergies are especially prone to exercised-induced asthma, said Drs. Gentile and Hagen.

"Chemicals and allergies can be a trigger," Dr. Hagen said. "In hockey, they talk about the Zamboni effect," asthma attacks triggered by fumes from the machine that cleans the ice between periods.

A longer, more vigorous warmup followed by a rest period will reduce the likelihood of an asthma attack during a game or competition, Dr. Davenport said.

Skiers and other winter athletes can reduce the likelihood of an asthma attack by wearing a mask, Dr. Hagen said. The mask makes the air the athletes breathes warmer, and thus less likely to irritate the airways.