A few well-controlled scientific studies have been published suggesting the possibility of pheromones in humans. The best-studied case involves the synchronization of menstrual cycles among women based on unconscious odor cues (the McClintock effect, named after the primary investigator, Martha McClintock, of the University of Chicago). This study proposes that there are two types of pheromone involved: “One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle”. This is analogous to the Whitten effect, a male pheromone mediated modulation of estrus observed in mice.

Other studies have suggested that people might be using odor cues associated with the immune system to select mates who are not closely related to themselves. (See Disassortative sexual selection) Using a brain imaging technique, Swedish researchers have shown that homosexual and heterosexual males’ brains respond differently to two odors that may be involved in sexual arousal, and that the homosexual men respond in the same way as heterosexual women. The study was expanded to include lesbian women and the results were consistent with previous findings meaning that homosexual women were not as responsive to male identified odors but their response to female cues was similar to heterosexual males.

According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation. Another study demonstrated that the smell of androstadienone, a chemical component of male sweat, maintains higher levels of cortisol in females.

The scientists suggest that the ability of this compound to influence the endocrine balance of the opposite sex makes it a human pheromonal chemosignal. In 2002 a study published in the quarterly journal Physiology and Behavior showed an unnamed synthetic chemical in women’s perfume appeared to increase intimate contact with men. The authors hypothesize, but do not demonstrate, that the observed behavioural differences are olfactory mediated.

In 2006 it was shown that a second mouse receptor sub-class is found in the olfactory epithelium. Called the trace amine-associated receptors (TAAR), some are activated by volatile amines found in mouse urine, including one putative mouse pheromone. Orthologous receptors exist in humans providing, the authors propose, evidence for a mechanism of human pheromone detection.

Some body spray advertisers claim that their products contain human sexual pheromones which act as an aphrodisiac. In the 1970’s “copulins” were patented as products which release human pheromones, based on research on rhesus monkeys. Subsequent to that androstenone, axillary sweat, and “vomodors” have been claimed to act as human pheromones. Despite these claims, no pheromonal substance has ever been demonstrated to directly influence human behavior in a peer reviewed study.