A hormone known as “the love hormone” prompts men in relationships to keep their distance from other women who are attractive, new research suggests.

Oxytocin, which is known to contribute to pair-bonding, encourages men to expand their personal “Don’t come near me” bubble when around an attractive woman — but only when those men are in relationships, researchers found. Single men were just as likely to get close to a pretty stranger whether or not they’d been dosed with oxytocin, according to a study published tomorrow (Nov. 14) in the Journal of Neuroscience. …

In both experiments, researchers found that relationship status mattered. Men dosed with oxytocin who had girlfriends or wives had bigger personal bubbles than other men. Single men and guys who got the placebo generally established themselves at about 20 to 24 inches (50 to 60 centimeters) away from the attractive experimenter. Oxytocin-dosed guys in relationships stayed about 28 to 30 inches (70 to 75 cm) away.