Children who become very distressed by family quarrels are more likely to develop psychological problems. But little is known about what happens beyond these behavioural reactions in terms of their biological responses. A new study by Universities of Rochester and Minnesota has found that such distressed children also have higher levels of cortisol, a stress hormone. "Our results indicate that children who are distressed by conflict between their parents show greater biological sensitivity to conflict in the form of higher levels of the stress hormone, cortisol," according to Patrick T. Davies, professor of psychology at Rochester, who led the study. "Because higher levels of cortisol have been linked to a wide range of mental and physical health difficulties," it "may help explain why children who experience high levels of distress when their parents argue are more likely to experience later health problems," he said. Researchers studied 208 primarily Caucasian six-year-olds and their mothers to determine whether children who showed specific behaviour patterns of reacting to conflict also had changes in cortisol levels during simulated phone arguments between their parents, said a joint release of these universities. They measured children's distress, hostility, and level of involvement in the arguments, and received reports from the mothers about how their children responded when parents fought at home. Cortisol levels were measured by taking saliva samples before and after the conflicts in the lab. Children who were very distressed by the conflicts in the lab had higher levels of cortisol in response to their parents fighting. Children's levels of hostility and their involvement during the arguments weren't always related to their levels of cortisol, the study found. The study will appear in the November/December issue of Child Development.