Chemicals that seem to act as sex-specific signals tickle the brains of gay men and straight women in a similar way. Using brain scans, Swedish researchers had found that women getting a whiff of the steroid derivative androstadienone, found in sweat, experience increased blood flow in a part of their hypothalamus known to release sexual hormones. Male sniffers responded instead to an estrogen derivative. Now the group has observed that in gay men the same brain location, called the peroptic area, responds to androstadienone rather than the estrogenlike steroid. Further experiments are needed to conclude that these activation patterns reflect sexual attraction, as opposed to discriminating between genders, or that the responses are innate or learned, cautions Ivanka Savic of the Karolinska Institute in Stockholm, co-author of the report in the May 17 Proceedings of the National Academy of Sciences USA.

Indeed, olfactory response may be more sensitive to sexual orientation than brain scanning can resolve. In the September Psychological Science, researchers from the Monell Chemical Senses Center in Philadelphia will report how they collected armpit sweat from straight and gay men and women. The outcomes were not as simple as “prefers men” or “prefers women.” All groups except gay men preferred the scent of lesbians to that of gay men, for example. Still, the work adds evidence for sexbased differences in odor production and preference.