Women who are having a heart attack are less likely to get bystander CPR and more likely to die, according to a new study — and it may be because people are reluctant to touch women’s chests.

A new study looked at 20,000 cases of cardiac arrest and found that 39 percent of women who had heart attacks in a public place received CPR, compared to 45 percent of men. Possibly as a result, men were 23 percent more likely to survive. The results were discussed at the American Heart Association conference in Anaheim, California, and were reported by The Associated Press. The study was funded by the National Institutes of Health and the Heart Association.

Cardiac arrest happens when the heart stops pumping. Administering CPR, or cardiopulmonary resuscitation — an emergency procedure that involves pressing on the chest repeatedly to restore blood to the brain and heart — can help survival odds until doctors can administer medication to try to restart the heart. More than 350,000 Americans suffer cardiac arrest in a place that’s not a hospital.

The researchers don’t know exactly why rescuers were less likely to help women. But because there was no difference in CPR rates for women who had cardiac arrest at home, where the victim knows the rescuer, they think maybe the cause is fear of touching unknown women. “It can be kind of daunting thinking about pushing hard and fast on the center of a woman’s chest,” said Audrey Blewer, a University of Pennsylvania researcher who led the study, according to the AP. CPR training may be biased in subtle ways, Blewer continued. For example, even practice mannequins are usually male torsos.

It’s possible rescuers worry about touching women’s breasts or moving a women’s clothing, according to another study author, Benjamin Abella at the University of Pennsylvania. “This is not a time to be squeamish, because it’s a life-and-death situation,” Abella said, according to AP.

2:09 p.m. 11/13/2017 Correction: An earlier version of this article incorrectly stated that defibrillators work when the heart stops pumping. Defibrillators treat irregular heart rhythms, but do not work when the heart has stopped entirely.