According to a study from universities in England, women who have more than two kids are perceived to look older, less healthy and less attractive than those with more children, Newsweek reports.

In the study, which is published in the American Journal of Anthropology,researchers had 571 men and women judge the faces of three groups of moms: women with one or two children, women with four to five children, and women with seven to nine. In order to avoid any bias, a computer program created «average» faces of post-menopausal women after researchers collected pictures of real moms.

The results: Even if the women were close in age, the volunteers consistently judged those with more kids to look older. And those with seven to nine kids were most likely to be marked as looking older, less attractive and less healthy.

Based on previous studies, researchers speculate that the link between moms with more kids and moms perceived to look older might have to do with the «oxidative stress» involved with carrying and delivering each child. Newsweek reports that oxidative stress happens when there is an imbalance between the production of free radicals—molecules created during pregnancy that can damage DNA and cells—and the body’s capacity to fight off their effects. Plus, studies have found that the placenta is an ideal place for free radical production, and that it actually peaks during the second trimester. As a result, more pregnancies mean more oxidative stress, leading women with more than two children to appear to age at a faster rate.