If you’ve noticed a faint, waxy, slightly grassy smell around an older relative — or started catching it on yourself somewhere past 40 — you’re not imagining things, and it isn’t a hygiene problem. It has a name, a known chemical cause, and a body of research behind it.

This guide walks through what the science actually says: why the smell shows up with age, why scrubbing harder doesn’t fix it, and which habits and ingredients have real evidence behind them.

It Has a Name: 2-Nonenal

The compound responsible is called 2-nonenal, an unsaturated aldehyde with a greasy, grassy odor. It was first isolated and linked to aging in a 2001 study published in the Journal of Investigative Dermatology by Japanese researchers Shinichi Haze and colleagues. Their team analyzed the body odor of subjects between 26 and 75 years old using gas chromatography and found 2-nonenal only in participants aged 40 and up — it simply wasn’t present in younger skin at all.

A separate 2010 study from the Japanese Society of Anti-Aging Medicine found detectable 2-nonenal in roughly 7 out of 10 participants over 40. In Japan, where this research originated, the phenomenon has its own word: kareishū, or “aging odor.” It’s taken seriously enough that an entire category of cleansing products has been built specifically to target it.

Why It Happens: The Skin Chemistry of Aging

2-nonenal isn’t caused by sweat glands working harder, and it isn’t bacterial in the way regular body odor is. It comes from the skin’s oil (sebum) itself.

As skin ages, two things change: antioxidant enzyme activity naturally declines, while levels of lipid peroxides — reactive molecules that break down fats — rise. At the same time, the skin’s surface lipids shift, accumulating more omega-7 monounsaturated fatty acids, particularly palmitoleic acid.

When lipid peroxides oxidize those omega-7 fatty acids, the byproduct is 2-nonenal. The Haze study found a direct correlation: the more omega-7 fatty acid and lipid peroxide activity in someone’s skin, the more 2-nonenal showed up in their body odor. Later biosensor research (published in Analytical Sciences, 2023) confirmed the same oxidative pathway and noted that 2-nonenal concentrations track fairly consistently with age rather than with activity level or perspiration.

That’s the key distinction from regular sweat odor: this smell comes from an oxidation reaction happening in the skin’s oil layer, all over the body — chest, back, scalp, behind the ears — not primarily from the underarms.

Common Misconceptions Worth Clearing Up

“It means someone isn’t washing enough.” Because 2-nonenal is fat-soluble and sits within the skin’s oil layer rather than on the surface, ordinary soap and water often aren’t enough to fully clear it, regardless of how frequently someone showers. Dan Wesson, a professor at the University of Florida College of Medicine, has noted publicly that the compound’s fatty composition makes it resistant to typical hygiene products.

“Perfume fixes it.” Fragrance masks the smell temporarily but doesn’t address the oxidation happening in the skin. Once the scent wears off, the underlying odor is still there.

“It’s a sign of poor health.” Not necessarily — it’s a normal part of skin aging tied to declining antioxidant capacity, not an indicator of disease. That said, sudden or unusual changes in body odor are always worth mentioning to a doctor, since some metabolic and skin conditions can also affect scent.

“Everyone finds it unpleasant.” A 2012 study in PLoS ONE found that most people don’t actually rate the “old person” scent as more unpleasant than younger body odor when smelled blind — the association with aging is largely learned, not purely sensory. Still, plenty of people would simply rather not carry an age-signaling scent, which is a reasonable and personal preference, not a hygiene failing.

What the Research Says Actually Helps

Because 2-nonenal comes from an oxidation reaction, the most evidence-backed strategies fall into two categories: reducing oxidation from the inside, and clearing oxidized lipids from the skin’s surface.

1. Antioxidant-rich foods

Diets higher in antioxidants may help limit the lipid peroxidation that produces 2-nonenal in the first place. Compounds that have shown scavenging activity against 2-nonenal or its precursors in published research include:

• Catechins in green tea
• Anthocyanins found in blueberries, blackberries, and blackcurrants
• Phenolamides isolated from eggplant, studied specifically for their ability to neutralize 2-nonenal and protect skin cells from its effects (published in a 2024 study in Antioxidants)

None of these are a cure on their own, but they support the same antioxidant pathway that naturally declines with age.

2. Cleansers formulated around polyphenol-rich plant extracts

Because 2-nonenal sits in the skin’s lipid layer, cleansing needs to do more than remove surface sweat — it needs to help break down oxidized oils. This is where persimmon extract has drawn specific research interest. Persimmon is unusually rich in tannin-type polyphenols, and a study published in the Journal of the Japan Association on Odor Environment found these polyphenols reduced measurable 2-nonenal levels on skin, attributing the effect to their antioxidant and odor-binding properties. It’s the same underlying chemistry that has made persimmon tannin (kakishibu) a traditional deodorizing and preserving agent in Japan for centuries, long before the biochemistry behind it was understood.

3. Washing the right areas, not just underarms

Since 2-nonenal is generated across the skin’s surface — especially the scalp, back, and chest, where sebaceous (oil) glands are more concentrated — a routine focused only on underarms and feet will miss most of it. A full-body wash that addresses oilier zones tends to make a bigger difference than spot-treating.

4. Sun and air exposure for fabric, not skin

For clothing and bedding rather than skin, UV exposure has a genuine deodorizing effect: sunlight helps break down surface oils and reduce bacterial load on fabric. It’s a low-cost habit worth pairing with proper laundering, especially for items that sit close to skin for long periods, like pillowcases and undershirts.

What to Look For in a Soap or Body Wash

If you’re evaluating products for age-related body odor rather than sweat-related odor, a few things matter more than fragrance strength. Look for polyphenol or tannin content — persimmon extract or green tea extract, which have documented antioxidant and odor-binding activity — paired with a gentle, non-stripping formula free of heavy synthetic fragrance, one you’ll actually use across your back, chest, and scalp, not just your underarms.

Frequently Asked Questions

The Bottom Line

Age-related body odor is a real, well-documented biochemical process, not a hygiene failure. Antioxidant-rich foods, full-body cleansing that reaches oilier skin zones, and cleansers built around polyphenol-rich plant extracts like persimmon are the approaches with actual research behind them.

This article summarizes published research for general educational purposes and isn’t medical advice. If you notice a sudden or unusual change in body odor, it’s worth mentioning to a doctor.