You shower, you feel clean, and by early afternoon something has quietly shifted. If that sounds familiar, here is the first thing worth knowing: it is not about how often you wash, and it is not a personal failing. It is chemistry, it happens to almost everyone as we get older, and it even has a name.
Meet nonenal, the compound behind the shift
In 2001, a team of researchers at the Japanese company Shiseido, led by Shinichiro Haze, published a study in the Journal of Investigative Dermatology with a memorable finding: a compound called 2-nonenal appears in human body odor and tends to increase with age. In their work it showed up in people aged around 40 and over, and was largely absent in younger participants.
The reason is elegant, if a little unfair. As we age, our skin produces more of a fatty acid called palmitoleic acid, while its natural antioxidant defenses gradually weaken. That combination lets skin lipids oxidize, and one of the byproducts is 2-nonenal, an aldehyde with a faint greasy, grassy scent. In Japan the resulting odor is common enough to have its own word: kareishu, or "aging scent."
None of this is a hygiene problem. It is simply what maturing skin does.
Why you are the last to notice
Here is the strange part. Our sense of smell adapts to scents we are around constantly, a process called olfactory habituation. Because your own nonenal is with you all day, your nose quietly tunes it out, while people around you may still register it. So the people most likely to notice are the ones closest to you, and the person least likely to notice is you. That is not carelessness, it is just how the nose works.
Why regular soap and deodorant do not solve it
Most soaps and body sprays work by adding fragrance on top. They smell fresh for an hour or two, then the perfume fades and you are back where you started, because the underlying compound was never dealt with. Antiperspirants target sweat, which is a different mechanism again. Nonenal comes from oxidized skin lipids, so masking it or blocking sweat does not remove it. To actually help, you need something that binds and neutralizes the compound itself.
What Japan discovered centuries ago
Long before nonenal had a name, Japan had an answer for the scent: persimmon. Tannin extracted from unripe persimmon fruit, Diospyros kaki, known as kaki tannin or kakishibu, has been used across Japan for centuries, from preserving and dyeing to keeping skin fresh.
Persimmon tannin has a molecular structure that lets it bind with odor compounds, including 2-nonenal, and neutralize them at the source rather than covering them up. Japanese makers have long valued it as one of the most effective natural deodorizing ingredients, and it remains the go to answer for kareishu in Japan today. Unlike perfume, it is not a mask. It works on the cause.
Simple ways to stay fresh through the day
A few practical habits go a long way, and most of them are free.
Choose a soap that neutralizes rather than masks. A persimmon based bar is made to bind odor compounds at the source, so freshness lasts on one wash instead of fading with the fragrance.
Give attention to where nonenal forms. It comes from skin lipids, so the chest, upper back, and the area behind the ears matter as much as the underarms.
Refresh your fabrics. Nonenal clings to clothing, so wash and air your knits and collars regularly, since even a clean body can pick the scent back up from a worn sweater.
Support your skin from the inside. Because nonenal comes from lipid oxidation, a diet richer in antioxidants and staying well hydrated is sensible everyday skin care, though it is a gentle helper, not a cure.
Keep it consistent. One simple daily habit beats an elaborate routine you will not keep.
Where Shibu comes in
We built Shibu on exactly this idea. One gentle daily bar made with Japanese persimmon, designed to neutralize odor at the source instead of hiding it, naturally derived, with no aluminium and no heavy fragrance. You use it like any soap, and freshness simply stays with you through the day.
If the nonenal story is new to you, you are in good company, most of the West has never heard of it. But now that you know what is happening and why, staying fresh becomes a lot simpler.
Explore the Shibu persimmon bar →(www.shibucare.com/products/shibu)
Key takeaways
- After around age 40, skin produces more of a compound called 2-nonenal, first documented by Shiseido researchers in 2001. It carries a faint greasy, grassy scent the Japanese call kareishu.
- It is driven by natural changes in skin chemistry, not by poor hygiene, and your own nose adapts so you rarely notice it yourself.
- Regular soap and deodorant mask the scent, they do not remove the compound.
- Japanese persimmon tannin, kakishibu, binds and neutralizes odor compounds like nonenal at the source, and has been used in Japan for centuries.
*A note: this article is general wellbeing information, not medical advice. If a change in body odor is sudden or unusual, it is worth speaking with a doctor, since it can occasionally point to something worth checking.*