Raising kids is tough under the best of circumstances. But throw chronic stress into the mix and mothers can lose their ability to parent effectively, according to a University of Rochester study to be published in Development and Psychopathology.

For the study, researchers observed 153 mothers and their 17- to 19-month-old children. Scientists monitored each mother’s heart rate with wireless electrocardiograph (ECG) devices to assess their stress levels while the children were left with a stranger for a few minutes. Afterward, researchers videotaped moms and their kids at play to see whether the mothers’ stress reactions influenced their parenting styles.

Findings showed these parents reacted to stress with two distinct patterns. Those with depressive symptoms had “hyperactive” stress reactions; in other words, they had higher heart rates that elevated further when their children were upset. These mothers demonstrated aggressive behavior—they spoke in angry tones of voice, used derogatory words and physically roughed up their kids during post-stress play.

The reason? Because these depressed moms were already overwhelmed by stress, they were oversensitive to new stressors and unable to handle stressful situations calmly, said Melissa Sturge-Apple, PhD, an assistant professor of psychology at the University of Rochester, and the study’s lead author.

Meanwhile, mothers struggling with issues such as poverty or crime-ridden neighborhoods exhibited “hypoactive” stress reactions. These moms’ heart rates started low and showed little increase in response to their children’s distress. In addition, these moms generally ignored their children during play afterward, and what little interaction they had with kids was overbearing.

Sturge-Apple said these mothers’ behavior was in response to the “cumulative wear and tear…of living in poverty and dangerous neighborhoods,” which erodes parents’ ability to react to everyday stresses.

“Stress gets under your skin,” Sturge-Apple said. “It literally changes the way a mother’s body responds to the normal demands of small children, and those changes make it much harder to parent positively.”

The takeaway? Finding ways to relax isn’t just good for parents, it’s also good for their kids too.

Click here to read more about how parental depression affects children.