When men are given the hormone oxytocin they are more likely to stay away from attractive women they don’t know and remain faithful in monogamous relationships, according to a new study published in The Journal of Neuroscience.

The hormone oxytocin, which is made in a part of the brain called the hypothalamus, plays a part in prompting childbirth, helps women nurse, and assists the human ability to form social relationships. It also encourages the bond between mothers and children and the bond between couples. A 2011 study said that oxytocin makes people act more courageous.

Prior research has also shown that oxytocin plays a role in developing trust, but experts had not, until now, discovered that it helps preserve monogamous relationships among humans.

During the new trial, René Hurlemann, MD, PhD, from the University of Bonn and team found that men who were given oxytocin were more likely to keep away from women they didn’t know when they were approached, even when they found them attractive. On the other hand, single men were not affected by the hormone.

For their study, the researchers gave nasal spray containing oxytocin to healthy, heterosexual men. Three quarters of an hour later, the men met an “attractive” female introduced by the experts. When the women moved closer to the men, or further away, the participants were questioned whether the woman was either at an “ideal distance” or a “slightly uncomfortable” proximity.

“Because oxytocin is known to increase trust in people, we expected men under the influence of the hormone to allow the female experimenter to come even closer, but the direct opposite happened,” said Hurlemann.

Oxytocin’s effect on the participants remained steadfast, despite whether the woman looked away from the men, or made direct eye contact. The results remained the same when the men were the ones moving away or closer to the female subject. All of the men, whether they had received a placebo or the oxytocin, reported the woman as being attractive. Therefore, the hormone did not alter the male’s feelings toward how she looked.

In a different part of the study, the experts discovered that oxytocin did not impact the space the men put between themselves and a male subject brought in by the researchers.