Why do 15 percent of all American children—and an even higher proportion among inner-city minority groups—develop asthma? No one knows. There is clearly a genetic predisposition, because parents with asthma are significantly more likely to have a child with asthma; a child whose older sibling has asthma is more likely to develop the disease as well. It’s also known that exposure to allergens, such as dust mites, cockroach droppings and dog and cat dander, raises the likelihood of developing asthma. But nobody knows when, and at what levels, exposure proves critical to developing the disease. Yale researchers have started vacuuming hundreds of houses and collecting tens of thousands of dust samples to try to answer these questions.

With the help of a $3.7 million, five-year grant from the National Institute of Environmental Health Sciences, a team led by Brian Leaderer, Ph.D., professor of epidemiology, has been going into the homes of around 1,000 infants living in and around Bridgeport, Hartford, New Haven and Springfield, Mass., to study how the home environment affects the development of asthma. The infants were selected at birth by finding mothers who already had a child with asthma in the home.

After taking lengthy medical and family histories and gathering information about the families’ houses, the teams then visit the homes and, using special vacuum cleaners, collect dust samples from critical spaces, including infant bedrooms, crib bedding, the room of the older asthmatic child, the main living room and kitchen. The dust is then checked for the presence of known allergens. Air is also sampled for fungi and mold and a passive monitor is placed in the home to measure gaseous pollutants, such as sulfur dioxide and tobacco smoke. Periodically, the team returns to collect additional samples and measure the airborne pollutants. Four times annually, the team gathers information about the infants’ respiratory health.

Dr. Leaderer hopes that his study will provide the first data that pinpoint which allergens at which point in early life can cause asthma to develop. “You have to understand the factors that cause asthma first,” he says, “and then you can develop effective mitigation strategies. We don’t know what exposure at what level over what period of time impacts the development of asthma.”