Day-to-day exposure to certain chemicals, pollutants and other environmental factors during the first year of life appears to raise a child's risk of developing asthma, according to researchers at the Keck School of Medicine of USC.

Growing up around weed killers, pesticides, fuel oil, soot and exhaust, cockroaches, as well as farm crops, dust and animals during the first year of life were linked to early asthma, according to study results published in Environmental Health Perspectives, the journal of the National Institute of Environmental Health Sciences. Babies who first attended daycare before age 4 months also were more likely to be diagnosed with wheezing early in life, but this did not lead to increased asthma.

"The first year of life seems uniquely important in terms of susceptibility to environmental triggers of asthma," says Frank D. Gilliland, M.D., Ph.D., professor of preventive medicine at the Keck School and a study author.

Understanding the causes of asthma early in life is especially important because persistent asthma early in childhood is associated with long-term health problems.
The research team conducted the case-controlled study within a large subset of children participating in the ongoing, USC-led Children's Health Study. Researchers collected information from mothers through a questionnaire.

Researchers with the Children's Health Study have monitored levels of major pollutants in a dozen Southern California communities since 1993, while carefully following the respiratory health of more than 6,000 students.

The researchers looked at 338 children who had been diagnosed with asthma before they turned 5 years old. They then matched those children to 570 asthma-free children of the same age who lived in the same communities. They also matched them according to whether the children had been exposed to maternal smoking while still in the womb.
They found that the risk of developing asthma before age 5 rose significantly with various exposures. Children exposed to weed killers before turning 1 year old, for example, had more than four-and-a-half times the risk of developing asthma before age 5 as non-exposed children. Children exposed to pesticides before age 1 had nearly two-and-a-half times the risk of developing asthma before age 5 as non-exposed children, while those exposed to cockroaches had just over twice the risk.

Children who attended daycare before 4 months of age had more than five times the risk of having wheezing problems before age 5 as kids who did not attend daycare.
The study was not designed to find out specifically why risk increased. In general, Gilliland notes: "The first year of life is a critical time period of lung development-both for immunity and airway structure. Others have shown that certain early-life exposures are important for asthma development."

In the case of daycare attendance, Gilliland theorizes that early and frequent exposure to respiratory infections in a daycare setting might raise early wheezing risk.

The researchers found that the more older brothers and sisters a child had at birth, the lower the child's risk of early asthma. Children who had four or more siblings, for example, were at a substantially lower risk of asthma than children with just one sibling. But they found nothing to indicate that other early childhood experiences such as exclusive breast-feeding or exposure to cats, dogs or other pets influence early asthma.