From Environmental Health News:

Cumulative risk assessment posits that multiple agents work together to induce disease and that multiple stressors therefore must be considered in order to gain a true understanding of why adverse health effects occur.  Now a small but growing number of scientists are pushing the envelope by investigating whether chronic psychological stress might be one of those factors, enhancing a child’s vulnerability to certain chemical exposures and contributing to effects that later show up as asthma, neurodevelopmental disorders, cardiovascular disease, obesity, cancer, and other problems. These researchers are also starting to identify biomarkers that may shed light on the mechanisms by which psychological stress acts on a child’s developing immune system and brain to modify or enhance the response to certain pollution exposures such as
traffic-related air pollutants and lead.

“We really don’t know how broadly such interactions may occur across chemicals. They are much more likely to occur when the chemical itself acts directly upon stress systems,” says Deborah Cory-Slechta, a professor of environmental medicine at the University of Rochester School of Medicine & Dentistry.

“We know some chemicals that interact with stress, such as lead exposure, but we don’t know which others do.”

Observations of links between stress and disease date back to at least the twelfth century, when the philosopher Maimonides cited emotional upset as a factor in asthma. But proving such links poses a significant challenge, says Malcolm P. Cutchin, a professor at the School of Medicine of the University of North Carolina at Chapel Hill. “Much has been hypothesized about the linkages, but we are just now beginning to tease out relationships and understand the processes,” Cutchin says. As researchers have learned more about techniques that can identify chemical and stress exposures in the human body, they have begun to apply techniques to estimate how people respond to stress and how that response, if it goes awry, can facilitate the development of diseases.