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What is nonenal smell? The biology behind aging odor

According to a 2001 study published in the *Journal of Investigative Dermatology*, 2-nonenal, the compound responsible for nonenal smell, was detected exclusively in subjects aged 40 or older. This greasy, grassy odor is a distinct and natural byproduct of biological changes that occur as we age, specifically the oxidation of fatty acids on the skin's surface.