With nearly a million variations on 400 smell receptors, everyone senses smell differently
A difference at the smallest level of DNA -- one amino acid on one gene -- can determine whether you find a given smell pleasant. A different amino acid on the same gene in your friend's body could mean he finds the same odor offensive, according to researchers at Duke University.
There are about 400 genes coding for the receptors in our noses, and according to the 1000 Genomes Project, there are more than 900,000 variations of those genes. These receptors control the sensors that determine how we smell odors. A given odor will activate a suite of receptors in the nose, creating a specific signal for the brain.