Wheezing. Coughing. Chest tightness. The frightening sensation of gasping for air. These are the typical symptoms of asthma, a leading cause of children's hospital admissions and a chronic health problem that leads to millions of visits to pediatricians' offices each year.

Asthma is characterized as an inflammatory disorder of the airways that is regulated by the immune system and triggered by an allergen or an upper-respiratory infection. During an asthma exacerbation, the air passages become clogged with secretions, narrowed by bronchospasms, and hypersensitive to all kinds of stimuli. The normal flow of air into the lungs is diminished. Fortunately, asthma exacerbations are reversible, either spontaneously or with treatment. If left untreated, however, they do occasionally lead to death. So besides being a very scary condition for children, asthma is also a potentially grave one.

In addition, the fact that the occurrence of childhood asthma has been on the rise for the past 30 years has become one of the great medical mysteries. This increase cannot be explained by changes in diagnostic criteria or by the development of more-accurate record keeping. Epidemiologists, scientists who try to determine what causes diseases in certain populations, have already ruled out those possibilities. The increase in the incidence of asthma has been noted all over the world. In some countries, even in regions within countries and among certain ethnic groups, this rise has been dramatic. In response to the trend, a special task force called the International Study of Asthma and Allergies in Childhood (ISAAC) has been formed to gather information that can help medical investigators determine what factors are involved.

Dr. Allan L. Frank, a board-certified pediatrician and the medical director of the Austin (Texas) Cystic Fibrosis Clinic at Children's Hospital, attributes the increasing prevalence of asthma today to a combination of factors. "There are lots of different theories out there," he says. "We're talking about air pollution and significant, dramatic changes in weather." In addition to environmental factors, the constant exposure of children in nurseries and day care to respiratory illnesses and colds may also be contributing to the problem. "This causes a sensitization of the airways," Dr. Frank says, "which in turn may cause children to have more of a tendency toward a hyperreactive airway. I think that the major reason why we see an increased prevalence of asthma in young children is because they have colds at an earlier age and much more frequently."

Between 1982 and 1995, the prevalence rate of childhood asthma in the United States rose dramatically -- from 40.1 per thousand to 74.9 per thousand. The highest rates have been found, for example, among Puerto Rican children in New York and inner city children in Chicago. While these examples correspond with generally lower socioeconomic levels, other countries have seen an increase in the prevalence of asthma among children of affluent families.

In addition to tracking the relative rates of asthma occurrence around the world, medical researchers are also looking at a number of risk factors that seem to be associated with asthma. Some of the factors they are studying the most closely include the following:

Heredity and genetics. A family history of asthma and other allergies, especially in the mother, is one of the strongest predictive markers for developing asthma. However, scientists believe that genetics alone cannot account for the steep increase in the prevalence of asthma in the relatively short time of 30 years, and that environmental factors must play key roles.

Maternal cigarette smoking. Numerous studies have suggested that the children of mothers who are heavy smokers have much higher rates of respiratory problems.

Air pollution. The possible role of ozone, sulfur dioxide, and other pollutants is under investigation.

Allergens. Asthma is essentially an allergic disease. Some of the most likely suspects for triggering asthma include dust mites (mites are tiny spiderlike creatures), cockroach debris, furry pets, bedding and flooring, molds, and certain foods.

Respiratory infections. Colds and other respiratory viruses may trigger the development of asthma in genetically susceptible children.

Of course, the prevention of asthma is the long-term goal. International research efforts, such as those being put forth by ISAAC, will continue to gather and evaluate information that ultimately will help identify all the risk factors and their relative significance. How to modify some of these factors will then become a question of public health policy.

If there is any good news, it's that the medical treatment of asthma has evolved dramatically in recent years. Most patients are able, through close collaboration with their physicians, to arrive at treatment regimens that effectively manage their symptoms. Though any medical condition is more difficult to accept when it affects a child, asthma does not have to rob children of normal childhood activities -- outdoors or indoors. In Dr. Frank's view, "Asthma is not a condition that has to limit or alter lifestyles as long as consistent follow-up is obtained and as long as the family has a good understanding of how problems should be dealt with."

Asthma Around the World

Some of the countries that have the highest rates of childhood asthma:

Some of the countries with the lowest rates of childhood asthma:

Inhalers

Metered dose inhalers, those "puffers" that are standard equipment in many kids' backpacks, are the most common means of delivery of asthma medications. Using an inhaler requires considerable hand-breathing coordination, however. Many children, as well as adults, end up receiving less than the available amount of the medication, and even when coordination and timing are on target, much of the medication ends up in the mouth and throat instead of the lungs. The use of spacers -- add-on rigid or collapsible cylindrical holding chambers -- enhances the effectiveness of inhalers, and most physicians strongly encourage their patients to use them.

In some parts of the world, the availability of spacers is limited and the cost is a hardship, so ingenious patients have devised their own novel devices. For example, some families in Africa have adapted soda bottles or plastic cups to use as spacers. In response to concern among physicians and health officials regarding the efficiency of these homemade versions, testing was done at the University of Cape Town, South Africa, comparing the different devices: commercially manufactured spacers, modified soda bottles, and cups. The soda bottles performed as well as the "real" spacers, and the cups were inferior to both devices.