Chinese scientists have found that gay men respond to male pheromones in the same way that heterosexual women do.
The study adds to growing evidence that same-sex attraction is at least partly biological.
The scientists from the Chinese Academy of Sciences sought to test recent evidence that people are influenced by sex pheromones in their sexual interactions with others.
They focused on assessing if two particular steroids, androstadienone (found in male sweat) and estratetraenol (in female urine), could be classed as sex pheromones by examining whether their smells unconsciously communicate gender information.
They showed men and women animations of non-gender specific outlines of walking figures while dosing them with the two steroids.
The researchers found that heterosexual females ignored estratetraenol but when they smelled the male steroid androstadienone they tended to perceive the walking figures as male.
By contrast, when heterosexual men smelled estratetraenol and looked at the same animated figures they perceiving the walkers as more feminine (with androstadienone having no effect).
Intriguingly, gay men had the same response as heterosexual women when they smelled androstadienone and perceived the figures as masculine, while not being affected by the smell of estratetraenol.
The researchers also found that the responses of bisexual or homosexual females fell in between that of heterosexual males and females.
The scientists noted that people could not consciously tell the difference between the two smells and so the effect must be an unconscious one.
“The results provide the first direct evidence that the two human steroids communicate opposite gender information that is differentially effective to the two sex groups based on their sexual orientation,” said the scientist.
“Moreover, they demonstrate that human visual gender perception draws on subconscious chemosensory biological cues, an effect that has been hitherto unsuspected,” they added.
The research was published in the journal Cell.