Duke University Medical Center researchers have found that genetic variants of odour receptors within the nose decide how a particular odour is perceived.
The researchers focused on two chemicals, androstenone and androstadienone, which are produced naturally by the body during the breakdown of the male sex hormone testosterone and are excreted in sweat and urine.
"We found that genetic variations of a specific odour receptor determine, to a significant degree, why the same chemicals smell pleasant or unpleasant to different people," Nature quoted Duke's Hiroaki Matsunami, Ph.D., assistant professor of molecular genetics and microbiology, as saying.
"These results demonstrate the first link between the functioning of a human odour receptor gene and how that odour is perceived," Prof Matsunami added.
Humans have about 400 odour receptors within the nose that perceive various odours or chemicals. Smells typically attach to their respective receptors, and the information is then sent to the brain for processing.
The researchers wanted to unveil why people respond differently when they smell these two sex steroid-derived chemicals. Hanyi Zhuang, a student in the Matsunami laboratory, tested all the known smell receptors and identified one that reacted strongly with the two chemicals.
Collaborating with Rockefeller University professors, the researchers asked 391 volunteers to inhale the two chemicals and explain what they smelled.
The whiff was described from no smell at all, to "vanilla and sweet" and "sickening and urine." DNA extracted from blood samples from each volunteer were sent to Matsunami's laboratory.
"After performing genetic analysis on each of the samples and correlating the results with the smell descriptions, we were able to link specific genetic variants with specific perceptions," Prof. Matsunami said.
"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," Prof Matsunami added.
Matsunami added that these results will probably support the existence of pheromones in humans. Pheromones are chemical signals between animals that communicate alarm, mating and navigation cues.
"The sex-steroid odours that we tested in humans act as pheromones in pigs, and there has been debate whether these same chemicals act similarly in humans. There is evidence that smelling these odours can affect the mood and physiological state of both men and women," Prof Matsunami said.
Prof Matsunami added it is likely that there are other receptors and receptor variants that may also play roles in how these two chemicals are perceived.
The study is published in the journal Nature.