What Is 2-Nonenal? The Science Behind Age-Related Body Odor
Key takeaways
- 2-nonenal is an unsaturated aldehyde found in body odor. In the 2001 study that named it, it appeared only in people aged 40 and over.
- It forms when certain skin oils oxidize, and it can bind to proteins on the skin.
- Not every study detects it, and other compounds such as nonanal also rise with age.
- It is a normal part of aging chemistry, not a sign of poor hygiene.
If you have ever noticed a faint, stale scent that seems to stay on skin or a shirt collar even after a shower, you are not imagining it. Researchers have spent more than two decades studying how body odor changes with age, and one compound comes up again and again: 2-nonenal.
This guide explains what 2-nonenal is, where it comes from, and what the published studies actually say, in plain language.
What is 2-nonenal?
2-nonenal (also written trans-2-nonenal) is an unsaturated aldehyde, a small molecule that evaporates easily and can be smelled at low levels. Its scent is usually described as greasy and grassy. The same molecule shows up in other places too, such as aged beer and cucumbers, where it contributes to their aroma.
In body odor research, 2-nonenal became well known after a 2001 study by Haze and colleagues, published in the Journal of Investigative Dermatology. The team analyzed body odor from 22 people aged 26 to 75. 2-nonenal was found only in participants aged 40 and older, and the title of the paper summed up the result: 2-nonenal tends to increase with aging.
"2-Nonenal newly found in human body odor tends to increase with aging."
Where does it come from?
Our skin is coated in a thin layer of natural oils. The 2001 study found that two things in these surface oils increased with age: omega-7 unsaturated fatty acids and lipid peroxides. When omega-7 fatty acids break down through oxidation, one of the products is 2-nonenal.
A 2010 study in the Journal of Biological Chemistry took this further. It showed that lipid peroxidation generates 2-nonenal in the body and that the molecule can attach itself to proteins. That helps explain why the scent can seem to cling.
Did you know?
You often cannot smell 2-nonenal on yourself. The nose adapts to familiar scents, so people tend to notice it on clothing or bedding before their skin.
Why can it linger after a shower?
A few reasons come together:
- It keeps forming. Skin oils are produced throughout the day, so new 2-nonenal can form after you wash.
- It binds to proteins. Research shows 2-nonenal can attach to proteins on the skin surface, which may make it harder to rinse away than sweat.
- Fabrics hold odors. Clothing and bedding absorb body odor compounds, and some fabrics release them less easily in the wash. We cover this in our guide to odor in clothes and bedding.
Daily life plays a part as well. In a small 2021 study, a high-fat diet and a stressful three-hour meeting both raised the amount of 2-nonenal measured on the skin.
Is it a hygiene problem?
No. Age-related odor shows up in people who shower every day. It reflects natural changes in skin chemistry, the same way skin texture and moisture change over time. Many people do not notice it on themselves at all, because our noses adapt to our own scent.
Research also suggests it is different rather than worse. In a 2012 blind test, 41 people rated body odor samples from three age groups. Samples from people aged 75 to 95 were rated as less intense and less unpleasant than samples from younger and middle-aged donors, although raters could still tell them apart.
What the research does not settle
Science is rarely a single study. A 2008 UK analysis of skin compounds in 25 adults did not detect 2-nonenal at all. It found that three other compounds, nonanal, benzothiazole and dimethyl sulfone, were higher in older participants. A 2024 study of 60 people aged 18 to 78 also pointed to nonanal as a reliable age marker. Diet, genetics and sampling methods may explain some of these differences.
The fair summary: skin chemistry changes with age, oxidized skin oils are a big part of that, and 2-nonenal is one of the best-studied compounds involved.
A consistent routine and clean fabrics tend to matter more than extra showers.
What can help
Because these compounds come from skin oils, a thorough, gentle wash is the starting point. Many people also like cleansers with plant polyphenols such as persimmon tannins and green tea catechins, which have been studied for their ability to bind odor compounds in lab settings. You can read more in Persimmon Tannins and Green Tea: What the Research Shows, or see every study we reference on our Research & Studies page.
What tends to help
- A thorough, gentle wash to clear skin oils away.
- Fresh clothing and bedding, since fabrics hold odors.
- A consistent routine rather than extra showers.
No soap is clinically proven to remove 2-nonenal, including ours. The Persimmon Body Bar is a cosmetic soap made to wash skin oils away, with a 60-day money-back guarantee so you can judge it for yourself.
Frequently asked questions
At what age does 2-nonenal appear?
In the 2001 study that named it, 2-nonenal was found only in participants aged 40 and over. Individual timing varies.
Can you smell 2-nonenal on yourself?
Often not. The nose adapts to familiar scents, so people tend to notice it on clothing or bedding before they notice it on their skin.
Does showering more often fix it?
Showering removes oils that have already built up, but skin keeps producing them. A consistent routine and clean fabrics tend to matter more than extra showers.
Sources
- Haze S, et al. 2-Nonenal newly found in human body odor tends to increase with aging. Journal of Investigative Dermatology. 2001;116(4):520-524.
- Ishino K, et al. Lipid peroxidation generates body odor component trans-2-nonenal covalently bound to protein in vivo. Journal of Biological Chemistry. 2010;285(20):15302-15313.
- Saito K, Tokorodani Y, Sakamoto C, Kataoka H. Headspace solid-phase microextraction/gas chromatography-mass spectrometry for the determination of 2-nonenal and its application to body odor analysis. Molecules. 2021;26(19):5739.
- Mitro S, et al. The smell of age: perception and discrimination of body odors of different ages. PLoS ONE. 2012;7(5):e38110.
- Gallagher M, et al. Analyses of volatile organic compounds from human skin. British Journal of Dermatology. 2008;159(4):780-791.
- Predicting chronological age via the skin volatile profile. Journal of the American Society for Mass Spectrometry. 2024.
