The reaction to a component of male sweat, the sex hormone androstenone, depends on genetics.

Scientists have long known there is a genetic link to odor perception, but it had not been proven that a particular gene caused varying perception of a specific odor. Now, genetics researcher Leslie Vosshall and research associate Andreas Keller with their collaborators at Duke University, have done it on androstenone, which is a derivative of testosterone.

The nose is lined with millions of smell receptor cells called olfactory sensory neurons, and each of these has one of about 400 different receptors, which will accept an odor molecule with a corresponding shape, like it does with pheromones. The molecule inserted into a receptor triggers signals to the brain and the perception of smell.

Vosshall and Keller’s study consisted of almost 400 volunteers doing a smell test with 66 different odors and measuring how the volunteers responded to each odor. The Duke University researchers were simultaneously studying all human genes responsible for smell receptor creation. Thus, they identified the gene responsible for making the receptor into which androstenone fits.

After merging the data, the collaborators discovered that people with a functional gene OR7D4 made the adequate receptors that accomodate androstenone. However, 30% of people had a variation of this gene, which resulted in a receptor that did not hold androstenone. The receptor difference was minute, yet caused profound results. Those in the first group were eleven times more sensitive to androstenone than in the second, thus providing the first proof that a specific gene is responsible for the perception of a specific odor.

Therefore, the study shows that our perceptions are subjective, based in biological and genetic differences.

Androstenone has been well known to the pig farming industry, because its smell makes female pigs in heat go into the mating position. Normally found in the saliva of male pigs, companies sell cans of androstenone to farmers and some others market it to men, alleging it attracts women.