Mothers and fathers have different stress responses to thoughts about their families, a new study indicates.

Although working mothers and fathers in the U.S. are almost as likely to think about family matters throughout the day, only for mothers is this type of mental labor associated with increased stress and negative emotions.

“I assume that because mothers bear the major responsibility for childcare and family life, when they think about family matters, they tend to think about the less pleasant aspects of it – such as needing to pick up a child from daycare or having to schedule a doctor’s appointment for a sick kid – and are more likely to be worried,” said study author Shira Offer, an assistant professor in the Department of Sociology and Anthropology at Bar-Ilan University.

The study relied on data from the 500 Family Study, a multi-method investigation of how middle-class families balance family and work experiences. The 500 Family Study collected comprehensive information from 1999 to 2000 on families living in eight urban and suburban communities across the United States. Most parents in the 500 Family Study are highly educated, employed in professional occupations, and work, on average, longer hours and report higher earnings than do middle-class families in other, nationally representative samples.

The paper, “The Costs of Thinking about Work and Family: Mental Labor, Work-Family Spillover, and Gender Inequality among Parents in Dual-Earner Families,” was presented at a meeting of the American Sociological Association.