A May 10, 2005 article in the New York Times, "For Gay Men, an Attraction to a Different Kind of Scent," by Nicholas Wade, stated:
"Using a brain imaging technique, Swedish researchers have shown that homosexual and heterosexual men respond differently to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as women.
The new research may open the way to studying human pheromones, as well as the biological basis of sexual preference. Pheromones, chemicals emitted by one individual to evoke some behavior in another of the same species, are known to govern sexual activity in animals, but experts differ as to what role, if any, they play in making humans sexually attractive to one another.
[G]ay men responded to the two chemicals in the same way as did women, Dr. Savic reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.
Dr. Savic said that she had also studied gay women, but that the data were 'somewhat complicated' and not yet ready for publication....
If human pheromones do exist, Dr. Savic's approach may allow insights into how the brain is organized not just for sexual orientation but also for sexuality in general....
The different pattern of activity that Dr. Savic sees in the brains of gay men could be either a cause of their sexual orientation or an effect of it. If sexual orientation has a genetic cause, or is influenced by hormones in the womb or at puberty, then the neurons in the hypothalamus could wire themselves up in a way that permanently shapes which sex a person is attracted to.
Alternatively, Dr. Savic's finding could be just a consequence of straight and gay men's using their brain in different ways. 'We cannot tell if the different pattern is cause or effect,' Dr. Savic said. 'The study does not give any answer to these crucial questions.'" May 10, 2005 NY Times
A May 10, 2005 article in the Proceedings of the National Academy of Sciences, (PNAS) "Brain Response To Putative Pheromones In Homosexual Men," by Ivanka Savic et. al., states in its Abstract:
The testosterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like steroid estra-1,3,5(10),16-tetraen-3-ol (EST) are candidate compounds for human pheromones. AND is detected primarily in male sweat, whereas EST has been found in female urine. In a previous positron emission tomography study, we found that smelling AND and EST activated regions covering sexually dimorphic nuclei of the anterior hypothalamus, and that this activation was differentiated with respect to sex and compound. In the present study, the pattern of activation induced by AND and EST was compared among homosexual men, heterosexual men, and heterosexual women.
In contrast to heterosexual men, and in congruence with heterosexual women, homosexual men displayed hypothalamic activation in response to AND. Maximal activation was observed in the medial preoptic area/anterior hypothalamus, which, according to animal studies, is highly involved in sexual behavior. As opposed to putative pheromones, common odors were processed similarly in all three groups of subjects and engaged only the olfactory brain (amygdala, piriform, orbitofrontal, and insular cortex).
These findings show that our brain reacts differently to the two putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes." [bolding added] May 10, 2005 PNAS