From schoolwork and peer relationships to meeting high parental expectations or living with conflict in the home, childhood can be a very stressful time. Scientists recently discovered a difference between stresses caused inside and outside the home.

Researchers measured levels of cortisol, a hormone that is produced when under stress, in children's saliva. Health records and interviews provide a reliable picture of the negative effects of unresolved stress:

Persistently high cortisol levels can be especially damaging in children. When stress continues over days, weeks, or years, many of their developing systems are put on hold, sometimes causing permanent damage. Unusually high cortisol levels from constant stress slow physical growth, delay sexual maturity, and can slow the growth of brain cells.

The cause of high cortisol levels has surprised researchers. Living in poverty, school work, or conflict with peers raises cortisol levels very little. According to researchers, "what really does affect them are family issues. When a family experiences some sort of trauma; father and mother have a fight, father leaves, or grandmother hits a kid; there is a physiological effect on the children. Their cortisol levels rise and stay high."

The continual absence of a mother or father in the home also has a major effect. The study shows that "girls between the ages of 9 and 16 are much more affected by the absence of their mother than are boys of this age. And infant boys but not girls respond to the absence of their father with abnormally low cortisol levels and slow growth."

Other findings include: Children react the same way each time parents fight or leave home. While adults learn to adapt to relentless stressful circumstances, "children always react as if they were encountering it for the first time." Many diseases suffered by middle-aged adults, like heart disease or high blood pressure, can be traced back to unresolved patterns of stress initiated during childhood.