Does your body odour change as you get older?
Yes, your body odour changes from around your forties onwards because a substance forms on your skin that is barely detectable in younger people. This is a normal biological process, not something you can entirely prevent.
Yes, body odour really does change with age, and a specific culprit has been identified: a substance called 2-nonenal. It is an unsaturated aldehyde with a greasy, grassy smell. Research showed that 2-nonenal is present exclusively in people aged 40 and older; in younger participants aged 26 to 39 it was not detectable at all.
How does this substance arise? The skin contains fatty acids. As we age, the level of a particular type of unsaturated fatty acids and oxidised fats on the skin surface increases. These oxidised fats trigger a kind of chain reaction of oxidation, similar to how food goes rancid. In this process, 2-nonenal is formed. Laboratory experiments confirm that this mechanism is correct: remove that oxidation and 2-nonenal does not form.
A smaller, exploratory study using a newly developed measurement system was also able to detect measurable differences in 2-nonenal between people in their twenties and people in their fifties. This strengthens the picture, but the study was too small to draw firm conclusions from.
There is also research that, alongside 2-nonenal, names four other volatile compounds as possible ageing markers. However, that claim is based on method-development research and has not been further substantiated with concrete data. Which of those four compounds actually play a role is not currently clear.
All claims are based on a limited number of studies (n=3 PMIDs). The core finding on 2-nonenal (PMID 11286617) has the most support, including a mechanistic explanation. The other studies (PMID 37447706 and 35956746) are small and exploratory.