The study people point to on this subject is Haze et al., 2001, published in the Journal of Investigative Dermatology. It was run by a research team at Shiseido, in Yokohama, Japan.
What they did. They collected body odour samples from volunteers aged 26 to 75 and analysed which compounds were present in each age group.
What they found. A compound called 2-nonenal showed up in the samples from subjects aged 40 and over, and was not detected in the younger group. They linked its formation to the oxidation of omega-7 unsaturated fatty acids on the surface of the skin.
Why it matters in a shower. 2-nonenal is oil-based. Water on its own does not lift an oil, which is the part most people recognise from experience: washing more often, or harder, changes less than it should.
What the study does not say, and neither do we:
- It does not say everyone over 40 develops a smell that other people notice.
- It does not measure how common that is in any population.
- It does not test any soap. Not ours, not anyone else’s.
- It does not show that removing this one compound changes how a person is perceived.
And it is not the only explanation. A change in body scent can come from bacteria living on the skin, from diet, from medication, from what your clothes are made of and how they are washed. A separate 1981 study by Leyden and colleagues looked specifically at the bacteria behind underarm odour, which is a different mechanism altogether. One compound is not the whole story.