Genes Help Govern Your Perception of Body Odor

Whether a sweaty man smells fragrant or foul to you may depend on your genes. Scientists have uncovered the first evidence to date that variations in a single gene can influence a person's perception of scent. The findings shed light on the science of smell and may help researchers explore how odorous molecules affect human behavior.

The human nose contains about 400 different odor receptors. Together, they can detect more than 10,000 different scents. Scientists have long known that people have varying perceptions of particular odors, but the factors that underlie these differences have been poorly understood.

"While many theories of the different perceptions of smell focus on culture, experience or memory, our results show that an important portion of this variability is due to an individual's genes," says Dr. Hiroaki Matsunami of Duke University Medical Center.

Collaborating with Dr. Leslie Vosshall's group at Rockefeller University, Matsunami and his team focused on two odorous steroids found in human sweat and urine. The steroids, androstenone and androstadienone, are related to the male sex hormone testosterone and are more highly concentrated in male than in female sweat. Previous studies had shown that androstenone can be perceived by different people as offensive, pleasant or odorless.

As reported in the early online edition of Nature on September 16, 2007, the scientists analyzed responses to 66 distinct odorant molecules, including cinnamon, lime, spearmint and the sweat-derived steroids. Their research was supported in part by NIH's National Institute on Deafness and Other Communication Disorders (NIDCD) and National Center for Research Resources (NCRR).

The scientists first measured how the 66 odorants interacted with cell-surface odor receptors in the laboratory. They analyzed more than 300 human odor receptors. One, OR7D4, showed a strong response to both steroids but not the other molecules.

The researchers then asked nearly 400 volunteers to sniff the 66 different scents and rate the intensity and pleasantness of each. Blood samples from the volunteers were analyzed to see how variability in the OR7D4 gene correlated with their perceptions of smell.

The scientists found that people who had 2 copies of the most common variant of OR7D4 were more likely to rate both of the sweat-based steroids as "extremely unpleasant." In contrast, people with 1 or 2 copies of another common variant were more likely to rate androstenone as smelling sweet like vanilla. Most people with rare variants in the OR7D4 gene had trouble detecting even high concentrations of the two steroids.

"These results demonstrate the first link between the functioning of a human odor receptor gene and how that odor is perceived," says Matsunami. He and his colleagues are now exploring whether the two steroids may act as pheromones, affecting human behavior as they do in animals. "There is evidence that smelling these odors can affect the mood and physiological state of both men and women," Matsunami says.

— by Vicki Contie