The “trust hormone” oxytocin could potentially play a role in fidelity, a small new study suggests.

A new study, published in the Journal of Neuroscience, shows that when men in relationships are given oxytocin, they stay a farther distance away from unknown, attractive women.

“Previous animal research in prairie voles identified oxytocin as major key for monogamous fidelity in animals,” study researcher Dr. Rene Hurlemann, M.D., Ph.D., of the University of Bonn, said in a statement. “Here, we provide the first evidence that oxytocin may have a similar role for humans.”

The study included 86 healthy, heterosexual men, and was broken into several parts. For one part, researchers administered either a nasal spray of oxytocin, or a placebo nasal spray to the men (about half of whom were single, while the other half were in committed relationships).

Then, 45 minutes later, an attractive woman came up to the men. In some cases, the men were asked to go toward the women; in others, the woman walked toward the men. The researchers instructed the men to say when their distance from her was an “ideal distance,” and when it made them feel “slightly uncomfortable.”

LiveScience reported that men who were in committed relationships and received the oxytocin kept a farther distance away from the attractive woman than the single men, or those who got the placebo instead of the oxytocin. Specifically, the men in relationships who got oxytocin preferred to stay 28 to 30 inches away from the attractive woman, compared with the 20 to 24 inches preferred by the single men and placebo-receivers.

The men in relationships stayed farther away from the woman than the single men no matter if the woman averted her gaze or looked directly at them. Researchers also found that the oxytocin didn’t seem to have any affect on the distance men kept from another man.

Earlier this year, a study conducted by researchers at Bar-Ilan University in Israel found that oxytocin may factor into the duration of a relationship. HuffPost Women reported on the study, which tracked couples over a six-month period. By the end of the period, the ones whose stayed together had oxytocin levels that remained pretty much the same throughout the study, while those who broke up were more likely to have oxytocin levels that decreased.

– Huffington Post