When a team of Duke researchers unveiled a study that showed the smell of sweaty men can actually range from stinky urine to sweet vanilla, they didn't anticipate the media attention that followed.
"I think it is a very relatable phenomenon that we studied," Andreas Keller-a postgraduate fellow at The Rockefeller University in New York City who contributed to the study-wrote in an e-mail. "When I talk to people about our project they very often find it easy to relate to and have some story."
Led by Hiroaki Matsunami, an assistant professor of molecular genetics and microbiology at Duke University Medical Center, the researchers published the finding on Nature magazine's Web site Sept. 16 and in its Sept. 27 issue. The study reported that the human perception of androstenone, a steroid found in male sweat and urine, varies by huge degrees depending on the genes of the odor receptor OR7D4.
"This is the first finding that any human odor receptor is associated with an actual sense of smell," Matsunami said.
The team started by exposing the receptors to various chemicals and studying the ensuing reactions, he said. OR7D4 responded to androstenone and caught researchers' eyes, he added.
When Matsunami presented his findings at a conference in 2005, he was approached by Leslie Vosshall, an associate professor of neurogenetics and behavior at Rockefeller, for a collaboration.
Matsunami said Vosshall's team had rounded up 400 New Yorkers and were studying how they reacted to different odors.
"They sent the genomic DNA [of the test subjects] to us, and we knew which receptor to look for," he said. "So we actually amplified that receptor gene and sequenced it, then found out that there are different variants of this gene."
Of the two variants, or alleles, one was determined to be more common than the other, the study showed. People with two copies of the more common allele perceived androstenone as having a strong odor, but those with one common allele reported androstenone as odorless. Those with two of the less common allele, however, reported androstenone as having a sweet odor like vanilla.
Researchers connected to the study have also been receiving e-mails from people around the world thanking them for doing the study and revealing personal secrets about their attraction to bodily smells, said Hanyi Zhuang, a graduate student in Matsunami's lab.
"They actually want to know if there is a genetic basis to that and if it's related to our study," Zhuang said.
For example, one e-mail from an anonymous female revealed that she was aroused by the smell of male sweat, Matsunami said.
The researchers said studies concerning OR7D4 will continue. Matsunami said his team wants to study the role of the receptor in human evolution. The receptor is also now being studied in various primates like chimpanzees and orangutans.
"We are planning follow-up studies in which we ask if the physiological effects of sniffing the related steroidal odor, androstadienone, correlate with variation in OR7D4," Vosshall wrote in an e-mail.
Keller said the continuing study of physiological effects will include only women because of their stronger responses to androstenone.
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