There’s a widely held notion that elderly people emit a particular — and easily recognizable — odor. While the smell has been described as stale, medicinal, musty, or simply “old person,” the Japanese have developed a more elegant term: kareishu. In one study, Japanese researchers traced the odor to a chemical compound called 2-nonenal. The compound is a byproduct of other chemical breakdowns and emits a “greasy” or “grassy” odor as the molecules exit the skin and are released into the air. Researchers discovered that 2-nonenal was the only odor compound that became stronger with age. They speculate the increase in 2-nonenal may have to do with the breakdown of omega-7 unsaturated fatty acids, possibly because of changes in metabolism as the body changes. Although the biological purpose behind "old person" smell is still unclear, some researchers believe that it's connected to a built-in age-detecting feature possessed by humans and animals. For instance, some animals can distinguish between older and younger animals by smell alone. It's possible that the ability to sniff out the smell of older animals meant that long-term survivors were revealed, and these survivors had a genetic advantage that boosted their odds of survival. In essence, the scent we've come to call "old person" smell could be an advertisement for superior genetic quality. It gives a whole new meaning to the term "silver fox.”
