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“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 whose presence became stronger with age.”