Androstenone is a 16-androstene class steroidal pheromone.
Androstenone was the first mammalian pheromone to be identified.
It is found in high concentrations in the saliva of male pigs, and, when inhaled by a female pig that is in heat, results in the female assuming the mating stance.
Androstenone is synthesized from androstadienone by 5α-reductase, and can be converted into 3α-androstenol or 3β-androstenol by 3-ketosteroid reductase.
It can have an unpleasant, sweaty, urinous smell, a woody smell, or even a pleasant floral smell.
There are two different genotypes that allow an individual to smell androstenone.
In small amounts, the odor is hardly detectable by most people.
The odor can be detected by people down to levels of 0.2 parts per billion to 0.2 parts in 100 million.
Some individuals who initially cannot smell androstenone can learn to smell it by repeated exposures to it.
In humans, androstenone also has been suggested to be a pheromone; but there is little scientific data to support this claim.
Humans lack the sensory cells that exist in other mammals needed to detect pheromones beyond a smell.
Some commercially available products are advertised using claims that they contain human sexual pheromones, including androstenone, and that they can act as an aphrodisiac.