According to the National Safety Council, children may be more susceptible to environmental exposures than adults and, because of their developing systems, particularly vulnerable to their effects. Asthma is a case in point. About 4.2 million children in the United States, and more than 12.4 million people total, are affected by asthma each year. A recent study, published in the American Journal of Respiratory and Critical Care Medicine concluded that 65 percent of asthma cases among elementary school-age children could be prevented by controlling exposure to indoor allergens and environmental tobacco smoke (ETS). By controlling biological contaminants (e.g., dust mites and cat allergens), asthma cases could be reduced by 55 to 60 percent.