Niamh Shackleton
If you've ever wondered why your great aunt Agnes smells a little bit different, there's a reason for it.
It's not because elderly people don't wash as much, and I'm pretty it's sure not because they're exercising more than ever - but it's because of a certain unsaturated aldehyde that makes up our body odor.
There are various different components that make up our personal body odor, but there's one part that increases as you age which gives you that kind of... old smell.
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It's called 2-Nonenal, and it's also an important aroma component of aged beer and buckwheat.
A 2001 study found that the 2-Nonenal component increases with age, therefore the older you are the more your odor changes.
As to how it smells exactly, the paper describes it as 'an unsaturated aldehyde with an unpleasant greasy and grassy odor'.
Researchers studied people aged 26 to 75 and then analyzed the findings to discover that 2-Nonenal was only in subjects aged 40 and over.
The study further explained: "Furthermore, analysis of skin surface lipids revealed that omega7 unsaturated fatty acids and lipid peroxides also increased with aging and that there were positive correlations between the amount of 2-Nonenal in body odor and the amount of omega7 unsaturated fatty acids or lipid peroxides in skin surface lipids.
"2-Nonenal was generated only when omega7 unsaturated fatty acids were degraded by degradation tests in which some main components of skin surface lipids were oxidatively decomposed using lipid peroxides as initiator of an oxidative chain reaction."
The study concluded that '2-Nonenal is generated by the oxidative degradation of omega7 unsaturated fatty acids' and that 2-Nonenal is linked to age-related changes to body odor.
Another thing that can change a person's body odor is Parkinson's Disease (PD) - a condition which typically occurs in those aged 50 and over.
While it's unlikely you'll know the smell yourself, those who have super sensitivity to smell might.
According to the American Parkinson's Disease Association (APDA), those with PD have increased rates of seborrheic dermatitis which causes patches of scaly, red skin due to over-secretion of oils from the sebaceous glands.
Scientists have analyzed some of the components of the sebum of people with PD and found a number of compounds that were present in larger amounts compared to those without the condition.
Following the study, sebum analysis is a potential biomarker for PD.