Stinky? It's not his sweat, it's your nose

By Julie Steenhuysen

CHICAGO (Reuters) - When it comes to a man's body odor, the fragrance -- or stench -- is in the nose of the beholder, according to U.S. researchers who suggest a single gene may determine how people perceive body odor.

The study, published online on Sunday in the journal Nature, helps explain why the same sweaty man can smell like vanilla to some, like urine to others and for about a third of adults, have no smell at all.

"This is the first time that any human odorant receptor is associated with how we experience odors," Hiroaki Matsunami of Duke University in North Carolina said in a telephone interview.

Matsunami and colleagues at Duke and Rockefeller University in New York focused on the chemical androstenone, which is created when the body breaks down the male sex hormone testosterone.

Androstenone is in the sweat of men and women, but it is more highly concentrated in men. How one perceives its smell appears to have a lot to do with variations in one odor receptor gene called OR7D4.

"It is well known that people have different perceptions to androstenone. But people didn't know what was the basis of it," Matsunami said.

To find out, researchers in Matsunami's lab tested sweat chemicals on most of the 400 known odor receptors used by the nose to sniff out smells and chemicals.

They found the OR7D4 gene reacted strongly with the sex steroid androstenone. Next, they tested whether variations in this gene had an impact on how people perceived the smell of androstenone in male sweat.