The ‘love hormone’ oxytocin may encourage fidelity by prompting men in relationships to keep their distance from attractive women, a study has found.

German researchers found that men in monogamous relationships who were given an oxytocinnasal spray stayed about four to six inches farther away from an attractive, woman they didn’t know, compared with men in monogamous relationships who received a placebo.

The oxytocin spray had no effect on the distance that single men chose to keep between themselves and the attractive woman, MyHealthNewsDaily reported.

“The results suggest the hormone promotes fidelity in humans,” said researcher Dr Rene Hurle­mann, of the University of Bonn.

The findings agree with previous research conducted on prairie voles, which suggested the hormone plays a role in pair-bonding.

In humans, oxytocin has been found to promote bonding between parents and children, increase trust, and reduce conflict between couples.

Earlier this year, a study found that couples with high levels of oxytocin in the early stages of a relationship were more likely to be together six months later than couples with lower levels of the hormone. However, until now, there has been no evidence that a dose of oxytocin given after a couple gets together contributes to the maintenance of the relationship.

The study involved 57 heterosexual males, about half of whom were in monogamous relationships.

After receiving either a dose of oxytocin or placebo, participants were introduced to a female experimenter who they later described as “attractive”. The experimenter moved towards or away from the men, and they were asked to indicate when she was at an “ideal distance” away, as well as when she moved to a distance that felt “slightly uncomfortable”. The effect of oxytocin on men was the same regardless of whether the woman maintained eye contact, or averted her gaze.