Around the age of 40, human skin begins producing a compound most people have never heard of: 2-nonenal. It is the molecule behind what is often called the “aging smell” — a faint, greasy-grassy odor that clings to skin, collars and pillowcases, and that ordinary soap does not remove.
Where nonenal comes from
As we age, the fatty acids on the surface of the skin change. Omega-7 fatty acids increase, and when they oxidize they break down into 2-nonenal. Japanese researchers first documented the compound in 2001, which is why most of the practical solutions for it come from Japan.
Three things make nonenal different from ordinary body odor:
- It is not caused by sweat or bacteria. Antiperspirants and antibacterial washes miss it entirely.
- It is lipid-based. It sits in the skin’s oil layer, so water and standard surfactants slide right past it.
- You usually cannot smell it on yourself. Olfactory adaptation means the people around you notice it years before you do.
Where it shows up first
Nonenal concentrates where skin oil is densest: the back of the neck, behind the ears, the chest and upper back. That is why the smell lingers on pillowcases, hat bands and shirt collars even straight out of the wash.
What actually works against it
Because nonenal is an oxidized lipid, the compounds that neutralize it are tannin-rich antioxidants. The best documented is kakishibu, fermented Japanese persimmon extract, which binds and breaks down nonenal on contact. It is the reason persimmon soap has been the standard answer in Japan for decades. We explain the extract in detail in our kakishibu guide, and compare all the options in 7 ways to get rid of nonenal.
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Frequently asked
At what age does nonenal start?
Production measurably increases from around age 40 in both men and women, and rises with each decade.
Does diet help?
Antioxidant-rich diets and exercise may slow the oxidation that creates nonenal, but no diet removes the compound already sitting on the skin.
Can perfume cover it?
Briefly, and the mix is usually worse than either smell alone. Removing the lipid layer it lives in works better than masking it.