Women in love seem to lose the ability to recognise body odour of other male friends while recognising the scent of their man remains intact.
To reach the conclusion, Johan Lundstrom and Marilyn Jones-Gotman of McGill University in Montreal, Canada, quizzed a group of 20 young women with boyfriends to fill in a Passionate Love Scale questionnaire to find out just how much in love they were.
Meanwhile, the women's partners and male and female friends slept for a seven nights in a cotton T-shirt with pads sewn into the underarms to soak up their sweat.
During the study, each female volunteer was asked to pick out their lover's or a friend's T-shirt from three garments, two of which had been worn by strangers, reports the New Scientist.
The women's scores on the Passionate Love Scale made no difference to their ability to recognise a lover's shirt, or that worn by a female friend. But those who were more deeply in love were less good at distinguishing a male friend's odour from those of strangers.
The study has been published in the journal Hormones and Behavior.