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title: What Is Nonenal? Age-Related Body Odor Explained | Kiyo Clinical
canonical: https://kiyoclinical.com/pages/what-is-nonenal
---

# What is nonenal? The age-related body odor no one warned you about

## The short answer

2-nonenal is an odor compound your skin starts producing from around age 40. As hormone levels shift, the fatty acids on your skin's surface oxidize more easily — and one of the byproducts is nonenal, which has a persistent, greasy-grassy smell. In Japan, where it was first identified, it's known as *kareishū* — often translated as "aging odor."

Two things make nonenal different from ordinary body odor: it isn't caused by sweat or bacteria, and it isn't water-soluble. That's why it can linger on collars, pillowcases, and skin even with careful hygiene.

## Why it starts around 40

With age — and especially with hormonal transitions like perimenopause, menopause, and andropause — skin produces more omega-7 fatty acids while its natural antioxidant defenses decline. When those fatty acids oxidize, nonenal forms. This is a normal change in skin chemistry, not a hygiene problem.

## How to tell if you have it

- Your body odor has changed in character since your 40s — less sharp, more "greasy" or "musty."
- The smell lingers on pillowcases, hats, and shirt collars even after washing.
- Deodorant doesn't seem to address it — because it forms on skin all over the body, not just underarms.
- You notice it most behind the ears, on the chest, back, and scalp.

## Why regular soap and deodorant don't work

Ordinary cleansers remove sweat, dirt, and bacteria. Nonenal binds to the skin's lipid layer and resists rinsing. Deodorants and fragrances layer scent on top, which can make the combination worse.

## What actually works: persimmon tannin

Tannin extracted from Japanese persimmon (*Diospyros kaki*) chemically binds to nonenal and neutralizes it on contact. Used daily in a wash-off format, it removes the compound at the source rather than masking it.

## A simple routine

1. Wash daily with a persimmon-tannin soap, focusing on chest, back, behind the ears, and other odor-prone areas.
2. Let skin dry fully before dressing — nonenal clings to damp fabric.
3. Wash bedding and collars regularly in warm water.
4. Be patient: most people notice a difference within one to two weeks of daily use.

## Product

- [Persimmon Deodorizing Soap](https://kiyoclinical.com/products/persimmon-odor-defense-bar)
- [The Science](https://kiyoclinical.com/pages/science)