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The Nonenal Research Index: Every Human Study on Age-Related Body Odor

2-Nonenal gets cited constantly and read rarely. This is every peer-reviewed human study we could find on it, what each one actually measured, and an honest account of the gaps — including the one directly under our own product.

Disclosure: The Soap Digest is owned by the same company that makes TanniBar. We rank it first and we earn money when you buy it. Every other brand here is linked without payment, and we try to describe each one fairly. Check the facts for yourself. How we handle this.

The molecule 2-nonenal is cited far more often than it is read. It turns up in product copy, in news write-ups about “old person smell”, and in a great many blog posts that all seem to be paraphrasing the same single paper from 2001 without having opened it.

So we opened them. This page is an index of the peer-reviewed research on 2-nonenal as it relates to human age-related body odor: what each study measured, how many people were involved, and — the part usually left out — what it does not show. It includes the gap sitting directly underneath our own product.

How we built this index

Stating the method matters more than the conclusion, because it lets you check us.

On 20 September 2026 we queried PubMed via the NCBI E-utilities API with these searches, then read the abstract of every result:

• "2-nonenal"[TIAB] AND (odor OR odour OR skin OR aging OR ageing)[TIAB] — 80 results
• "nonenal"[TIAB] AND "body odor"[TIAB] — 10 results
• "aging odor"[TIAB] OR "age odor"[TIAB] OR "old person smell"[TIAB] — 5 results
• persimmon AND tannin AND (odor OR deodor* OR malodor)[TIAB] — 0 results
• "persimmon soap" — 0 results
• persimmon AND "2-nonenal" — 0 results

Inclusion: studies measuring 2-nonenal in or from human skin, characterising its formation, developing a method to measure it, or testing something intended to reduce it. Exclusion: the large food-science literature where 2-nonenal appears as a flavour compound in beer, coffee, meat and cucumber, and the much larger literature on 4-hydroxy-2-nonenal, which is a different molecule (see below). After filtering, fourteen records were on topic.

We are not a systematic review, we did not search Embase, Scopus or the Japanese-language literature, and a company-funded study that was never published in a journal would not appear here at all. Treat this as a careful reading list, not a final word.

Re-checked 29 September 2026. No new paper on 2-nonenal and human body odor has been published since this page went up — the nonenal AND "body odor" search returns the same records it did nine days ago. The re-check did, however, find three on-topic papers the first pass missed, all of them published before it: Minami 2024 and Kim and Bae 2022 on measurement, and Kim 2025 on scavenging. Two of the three were alluded to in the original text without being cited, which is the sort of thing this page exists to not do. They are named in full below. We also added Murphy 2002, which is not a 2-nonenal paper at all and sits outside the inclusion criteria above — it is here because it constrains how every other result on this page can be interpreted, and the section explains why.

Re-checked 8 October 2026, and we owed a correction. The "2-nonenal"[TIAB] AND "body odor"[TIAB] search still returns ten records, the same ten as in September, so no new paper on this molecule and human body odor has appeared. But on going back through that set record by record, one of the ten had never been named on this page: Itoh and colleagues (2020), a gas-sensor study. It is now in the measurement section below. A page that claims to have read every abstract in a search should not be missing one of ten, and the omission is ours rather than the search’s. All ten are now cited by name. Two further searches were run the same day: "persimmon tannin"[TIAB] AND skin[TIAB] returned three results, which turn out to matter and are dealt with under the gap below, and "persimmon soap" returned zero for the fourth time since this page went up.

Re-checked 3 November 2026, and we owed another correction — a larger one. The core "2-nonenal"[TIAB] AND "body odor"[TIAB] set still returns the same ten records, unchanged in count and membership for the fifth check running. But a different search on our own list, "aging odor" OR "age odor" OR "old person smell", also returns five records today exactly as it did in September, and two of those five had never been named on this page. A stable count hid a changed set. Both are now cited in full below: Jin and colleagues (2025) on a bacterial culture that scavenges the compound, and Zhang and colleagues (2025) on a fabric that destroys it — the second of which this page had been alluding to for weeks without citing, which is the precise failure it exists to avoid. The other three records in that set are the eggplant paper below and two false friends: a study of the scent of a Tahitian liverwort, and one on attractive volatiles in aged male mouse urine.

Four further searches were run the same day, and they are set out in the washing section below because they bear on one question more than any other.

What is well established

2-Nonenal is in human body odor and tracks with age. Haze and colleagues (2001) analysed the body odor of subjects aged 26 to 75 by headspace GC/MS. 2-Nonenal was detected only in subjects aged 40 or older. In the same work, ω7 unsaturated fatty acids and lipid peroxides in skin surface lipids also rose with age, and the amount of 2-nonenal correlated positively with both. Degradation tests confirmed 2-nonenal was generated when ω7 unsaturated fatty acids were oxidatively broken down.

This is the paper everything else cites, so two things are worth saying plainly. It is genuinely good work and its central finding has held up. It was also conducted by researchers at Shiseido, a cosmetics company — which does not make it wrong, but does mean the foundational paper in this field came from industry, and you should know that when you see it cited as neutral background.

It rises with age in women as well as men. Kimura and colleagues (2016) built a passive flux sampler that sits on the skin and traps emitted gases for GC/MS. Emission flux of 2-nonenal increased with age in both male and female volunteers. The same study found diacetyl — long described as a “middle-aged male odor” — peaked in the 30s and declined after 40, and was not male-specific either. They fixed the nape of the neck as the sampling site because emission varied sharply by body location and the nape has dense sebaceous and eccrine glands.

That last detail is the practical one, and it is why every sensible washing guide tells you to start at the neck and scalp rather than the armpits.

The formation mechanism is characterised. Ishino and colleagues (2010), in the Journal of Biological Chemistry, showed that trans-2-nonenal is generated endogenously during the peroxidation of polyunsaturated fatty acids, and that it covalently modifies proteins — reacting preferentially with lysine residues to form a specific adduct. They raised a monoclonal antibody against it and detected the adducts in living tissue. This is the study that moves 2-nonenal from “a smell people noticed” to “a documented product of lipid peroxidation in the body”.

The tension nobody mentions

Here is something that should be better known, because it complicates the tidy story.

Hayashi and colleagues (2003) measured skin surface lipids in an older group (mean age 83.7) against a younger group (mean age 22.2). Free fatty acids and squalene were significantly lower in the older group. Linoleic acid composition fell by 40%. And monounsaturated acids including palmitoleic acid — the ω7 precursor from which 2-nonenal is formed — also decreased significantly with age. Haze 2001 reported the opposite direction in a group starting at 40, and the two studies sampled different parts of life — a tension we unpack in what age this smell actually starts.

So the precursor goes down while the odor goes up. The authors flagged this as interesting rather than resolving it. The likely explanation is that what matters is not how much precursor is present but how much of it is being oxidised, which depends on antioxidant capacity rather than raw lipid quantity. But that is an inference, not a finding, and anyone telling you confidently that “as you age you produce more nonenal precursor” is going beyond the published data.

How it gets measured

Six independent approaches now exist, which is part of why the age association is credible.

• Passive flux sampler + GC/MS — Kimura 2016. A sampler creates a headspace on the skin; trapped gases are extracted and quantified.
• Headspace SPME + GC/MS from a gauze wipe — Saito and colleagues (2021). Limit of detection 22 picograms on gauze, linear from 1–50 ng. They applied it to lifestyle variables including cosmetics use, food intake, smoking and stress load.
• Enzyme biosensors (“bio-sniffers”) — Iitani and colleagues (2023) built fluorescence sensors using aldehyde dehydrogenase and enone reductase 1, quantifying 2-nonenal vapour over 0.4–7.5 ppm with a detection limit of 0.23 ppm. The enone reductase version was far more selective.
• Semiconductive gas-sensor array + machine learning — Itoh and colleagues (2020), in Sensors. Eight metal-oxide sensors were used to pick out three compounds the authors group as age-related body odours — 2-nonenal, pelargonic acid and diacetyl — plus a fungal marker, against interference from car-interior gases (n-decane and butyl acetate), with principal-component and linear-discriminant analysis to reduce the signals and a k-nearest-neighbour classifier to score the separation. Discrimination between the target gases was, in the authors’ words, “nearly achieved”. The work was done at Japan’s National Institute of Advanced Industrial Science and Technology with a co-author at DENSO Corporation, which is worth stating: the application here is cabin air quality in cars, not skincare.
• Nanomechanical sensing — Minami and colleagues (2024), in ACS Sensors. A membrane-type surface stress sensor was used to discriminate 20 reported body-odor vapours by their sorption kinetics, and it separated trans-2-nonenal from other, chemically similar saturated aldehydes while also quantifying concentration. That last part matters: distinguishing 2-nonenal from its near-neighbours is the hard problem in any sensor approach, and it is why array methods like Itoh’s were suggestive rather than specific — Itoh’s own array was discriminating between four deliberately chosen target gases in a rig, not identifying one aldehyde in the open air.
• Adsorbent microextraction + GC/MS, sampled on the skin — Kim and Bae (2022) coated a wire with a composite adsorbent and exposed it directly to skin for in vivo sampling, alongside an in vitro version that sampled the headspace of a worn cotton T-shirt in a vial. Useful for two reasons beyond the chemistry: it treats trans-2-nonenal as one of five aging-associated skin VOCs rather than the only one, and it confirms that worn fabric holds enough of the compound to be measured off it.

And once, it was measured in a house rather than on a person. Liu and colleagues (2021), in PNAS, ran space- and time-resolved measurements of ozone and volatile organic compounds through an occupied California home with two adult inhabitants over an eight-week summer campaign. Indoor ozone averaged only 4.3 parts per billion, drifting in from outdoors, and even at that level they identified a family of compounds clearly being generated indoors by ozone-driven chemistry — 6-methyl-5-hepten-2-one, 4-oxopentanal, the C8–C12 saturated aldehydes, and nonenal. Two caveats belong on an index page: the paper names nonenal without specifying the isomer, so it cannot be quoted as a 2-nonenal measurement, and this is one house. What makes it worth the entry anyway is a control the authors did not have to run and did: ozone-driven production of the skin-lipid markers continued while both occupants were away for five days, and reacting ozone with the two residents’ own body surfaces was not enough to account for the yields. Skin oil transferred onto surfaces was doing the chemistry. We take the practical version of that apart in old person smell in a house.

Nothing here is a consumer device. If you see a product claiming to measure your nonenal at home, it is not using any of these. And the fabric result is the laboratory version of something readers report constantly — that the smell lives in clothes and furniture as much as on skin, which we deal with practically in getting it out of clothes and out of furniture. It is also the reason covering the smell and removing it are different operations, which we take apart in does Febreze remove body odor.

What has been shown to reduce it

This is the shortest section, and that is the point.

One human study. Willems and colleagues (2022) gave 14 middle-aged and older adults (nine male, mean age 55) New Zealand blackcurrant powder — 6 g/day providing 138.6 mg anthocyanins — for seven days in a crossover design, then sampled skin volatiles at the nape of the neck for one hour. Compared with control, emission of six skin VOCs including 2-nonenal was lower by more than 25%. Some other compounds rose.

Take it for what it is: fourteen people, one week, one sampling site, a commercially available supplement, and a measurement of emission rather than of whether anyone could smell a difference. It is the most interesting result in the field and it is nowhere near a recommendation.

Materials work exists but is not about people, and it is time this page named it. Zhang and colleagues (2025), in Langmuir, built a multilayer composite textile — manganese oxide loaded onto polyester, then aminated — in which the static charge generated by ordinary rubbing drives a catalytic reaction that breaks the aldehyde down, reporting 87.77% removal of 2-nonenal. Earlier, Lee and colleagues (2020) degraded trans-2-nonenal in solution using enzymes extracted from hen egg white, tracked by HPLC. Both destroy the actual molecule, which is more than most things sold for the purpose can claim. Both did it to a gas or a liquid in a laboratory. Nobody was washed and no odour was assessed.

The clearest recent example of that second kind is worth naming, because it is the nearest published analogue to the claim made for persimmon tannin. Kim and colleagues (2025), in Molecules, tested extracts of eggplant fruit, leaf, stem and root for 2-nonenal scavenging ability, identified the active compound as N-trans-feruloylputrescine, and then showed that the extracts reduced the reactive oxygen species and lipid peroxidation that 2-nonenal induced in skin cells. It is careful work and it demonstrates the mechanism cleanly.

It also shows exactly where this class of evidence stops. Everything measured happened in chemical assays and in cultured skin cells. Nobody was washed, nobody was smelled, and no odor was measured on a person. A plant polyphenol that scavenges 2-nonenal in a tube is a reason to run a human study, not a substitute for one — and that applies to eggplant and persimmon alike.

A second scavenger arrived in 2025, and it stops in exactly the same place. Jin and colleagues (2025), at Kyung Hee University, worked on Leuconostoc mesenteroides THF-10, a lactic acid bacterium isolated from oriental melon. The cell-free supernatant inhibited Staphylococcus epidermidis, S. aureus and Pseudomonas aeruginosa, suppressed biofilm formation, cut reactive oxygen species production by 39% at 20 µg/mL, and scavenged 73% of trans-2-nonenal in assay, with no toxicity in cultured keratinocytes. The authors conclude it has “potential for mitigating old age odor”, and potential is the right word: this is a bacterium in a flask meeting a molecule in a tube. It is a useful entry here for a reason beyond the chemistry, though — it is the one paper in this set that targets the odour-producing bacteria and the aldehyde at the same time, which is a different theory of the problem from the one a tannin bar is built on. Why those are separate problems is the subject of whether a fungal or bacterial infection can cause body odor.

One more analogue is worth adding, because it is a tannin and it works on the same chemistry Ishino described. Sobhy and colleagues (2025), in the International Journal of Biological Macromolecules, studied geraniin — a hydrolysable tannin — in bovine serum albumin incubated with glucose, glyoxal and methylglyoxal. Geraniin competitively bound specific lysine and arginine residues on the protein, preserving 85% of free lysine residues by steric hindrance, and trapped the reactive carbonyl species in the intermediate stage, suppressing downstream damage markers by 60–70%.

Read that against the formation mechanism above and the parallel is hard to miss: 2-nonenal’s documented reaction is with lysine residues on protein, and here a tannin defends lysine residues and mops up reactive carbonyls. That is the most mechanistically specific support we have found for the general idea behind a tannin soap. It is also a protein in a cuvette. The tannin is geraniin, not persimmon tannin; the carbonyls are glyoxal and methylglyoxal, not 2-nonenal; the matrix is bovine serum albumin, not skin; and nothing in it was smelled. It belongs on this page as a reason the mechanism is not absurd, and nowhere near a product claim.

What happens when you wash it off

Re-reading the r/Menopause thread this page was partly built on, one argument runs through it that none of the research above answers, and it is not a sceptic-versus-believer argument. It is three people reasoning about chemistry. One points out that a soap is rinsed away and whatever it did cannot last the rest of the day. Another replies that their skin stays fresh for about a day. A third asks how long anything applied to skin can possibly keep working, given that a soap is not a drug that stays in the body. Nobody is being unreasonable and nobody can settle it, because the measurement does not exist.

We went looking for it on 3 November 2026 and the result is worth stating precisely, because it is broader than the gap this page usually reports.

• nonenal[TIAB] AND soap[TIAB] returns zero records. Not zero trials — zero papers in which the two words appear together in a title or abstract at all. The persimmon-specific negative this page has reported since September is a special case of a much larger absence.
• "2-nonenal"[TIAB] AND (wash* OR bath* OR shower* OR cleans* OR soap)[TIAB] returns nine, walked one by one. Three are 4-hydroxy-2-nonenal papers. The remainder are a rat graft model, in vitro digestion of haemoglobin, a mouse colon study, a strawberry supplementation trial, meat chemistry, and a 1997 study in rabbit platelets. Not one measures this compound on skin that has been washed.
• "2-nonenal"[TIAB] AND (deodorant* OR deodoris* OR deodoriz*)[TIAB] returns seven, and every one is food or industrial — off-flavours in omega-3 oils, deodorising cattle by-products, removing fishy malodour from a seaweed, mango seed oil, sourdough rye bread, and the egg-white enzyme work above. None is about deodorising a person.
• "2-nonenal"[TIAB] AND (underarm* OR armpit* OR axillary OR axilla)[TIAB] returns zero. The molecule that an entire shelf of products is sold against has never been measured in the part of the body most people mean when they say body odour. That is also why underarm questions, including why one armpit smells worse than the other, belong to a different chemistry entirely.

So there is no published time course for 2-nonenal on skin after washing with anything — not a tannin bar, not another cleanser, not plain water. Any statement about how long an effect lasts, in either direction, is someone reasoning from first principles. Including this one.

What the mechanism does license is narrower and more useful than either side of that argument. 2-Nonenal is strongly oil-soluble, with an XLogP3 of 3.1, so it concentrates in an oil film and water alone will not lift it; a surfactant is the right class of tool for removing what is present. But Ishino 2010 showed a portion of it becomes covalently bound to protein, which is not a film and does not rinse. Put those together and you get a reasonable expectation that a wash removes the free compound sitting there at that moment, and no reason whatever to expect a residual effect once the water stops. A persisting effect is what a leave-on product claims, and a true soap is not one — which is the honest frame for the frequency question we work through in how to use persimmon soap, where the only thing actually measured is the cost of washing more often rather than the benefit.

The gap under our own product

We sell a persimmon tannin soap, and we rank it first on our persimmon soap comparison. So this section needs to be unambiguous.

There is no published human trial of persimmon soap for 2-nonenal or age-related body odor. On the day this page was published, "persimmon soap" returned zero PubMed results and persimmon AND "2-nonenal" returned zero.

What does exist is adjacent and worth reading honestly:

• Persimmon polyphenols do have measurable deodorising activity — Li and colleagues (2026) characterised their cooperative removal of ammonia and hydrogen sulfide in solvent systems. But ammonia and H₂S are basic and sulfurous gases neutralised by acid-base chemistry. 2-Nonenal is an aldehyde. Activity against one does not transfer to the other.
• Kakishibu’s protein-binding is documented — Tokin and colleagues (2021) showed fermented persimmon juice inhibits microbial enzymes through non-specific tannin–protein interactions. That is a real mechanism, and it is the honest basis for the “tannins bind things” story. It was demonstrated on cellulose-degrading enzymes in the context of wood and paper protection, not on skin.

• Persimmon tannin has been studied on skin exactly once, and it was not about smell. This is the sharpest way we have found to put the gap, and we only found it on the October re-check. Searching "persimmon tannin"[TIAB] AND skin[TIAB] returns three records. Two are not about skin in the sense you would assume: one is about peanut skins as a source of proanthocyanidins, the other about cognition in mice. The third is real: Sun and colleagues (2021), in the Journal of Cosmetic Dermatology, applied persimmon tannin extract to guinea pig skin and measured its effect on pigmentation. So the whole published record of persimmon tannin meeting living skin is one animal study about skin colour. Nobody has published what happens to odor.

• And the gap is wider than persimmon. This is the sharpest version we have found of it, added on the November re-check. The claim under every bar in this category is not really about persimmon at all — it is that tannins break 2-nonenal down. So we searched for tannins and the molecule together, with the stem wide open: tannin*[TIAB] AND "2-nonenal"[TIAB]. It returns five records, and we walked all five. They are a survey of volatiles across 29 cucumber cultivars, an analysis of guava leaf extract, a leaf-tea debittering process, the storage chemistry of faba bean flour, and a method paper on carbonyl compounds in wine. The two words co-occur in food and plant chemistry and nowhere else. No published paper examines a tannin of any kind acting on 2-nonenal in or on human skin. Not persimmon, not green tea, not oak, not any of them.

So the mechanism is plausible and the product evidence is absent. Both halves of that sentence are true, and we have written the whole site around saying so — see does persimmon soap actually work for the longer version.

Is this pseudoscience?

It is a fair question and it gets asked sharply. In September 2026 an r/Menopause thread titled “2-nonenal and skin changes” turned into an argument about exactly this, and the sceptical side made specific, technical complaints rather than vague ones: that the studies behind the claims have tiny samples, are not peer reviewed, and rest on participants’ subjective verbal reports; that nothing comes up when you search for it except advertising; and that naming a molecule lends false precision to a prejudice about older bodies.

Those complaints deserve a straight answer, and the answer is that they are aimed at two different claims that get sold as one. “2-nonenal is a real, age-associated skin compound” and “persimmon soap removes it” are separate propositions with very different amounts of evidence behind them. Almost every argument about this conflates them, in both directions.

On the molecule, the sceptical case does not hold up. Each specific objection fails against the record above:

• Tiny samples. The age association does not rest on a small study. Haze 2001 sampled subjects from 26 to 75; Kimura 2016 measured emission flux across ages in both sexes; Hayashi 2003 compared lipid profiles in two age groups. None of these is large by epidemiological standards, but they are not case reports either, and they agree.
• Not peer reviewed. Every paper named on this page is in a peer-reviewed journal. The formation chemistry was published in the Journal of Biological Chemistry (Ishino 2010), which is not a venue that prints marketing copy, and it did the unglamorous work — raising a monoclonal antibody, identifying a specific 2-nonenal–lysine adduct, detecting it in living tissue by mass spectrometry.
• Subjective verbal reports. This is the objection that most clearly misses. Essentially none of the molecule research asks anyone what they smell. It is gas chromatography, mass spectrometry, enzyme biosensors, surface-stress sensors and sensor arrays — six separate measurement approaches, from different groups, most of them unconnected to the soap trade. Itoh 2020 is the clearest illustration: a Japanese national research institute building a detector for 2-nonenal in car cabin air, with no cosmetic application in sight.
• It’s just a prejudice with a chemical name. The compound is identifiable, quantifiable and traceable to a specific reaction. That does not oblige anyone to find it disgusting, and the research itself is neutral on that; what it does rule out is that the smell was invented to sell something.

There is a stronger point available than any of those, and it is internal. This literature publishes results that are inconvenient for the sales story. Hayashi 2003 found the ω7 precursor declines with age, which contradicts the tidy “older skin makes more of the stuff” line used in marketing — we give it its own section above. The one human intervention anyone has published, Willems 2022, is a blackcurrant supplement, not a soap. A field organised to sell bars of soap would not keep producing findings like those.

On the product, the sceptics are substantially right, and we are not going to pretend otherwise. Taken as a description of the evidence for persimmon soap rather than for the molecule, the complaints in that thread are close to accurate:

• The most-cited human data is not a journal article at all. It is a 2001 Japanese cosmetics patent (JP2001-302483A, filed by inventors at Menard Cosmetics — company patent data, not peer-reviewed), and its human test used ten people per formula over two weeks, scored on a self-rated five-point scale with no odor measurement. “Small sample, not peer reviewed, subjective ratings” is a fair summary of it. We read it in full and set it out on does persimmon soap actually work.
• Those patent formulas were leave-on products — a mist, gel, lotion, aerosol and emulsion — not soap.
• "persimmon soap" still returns zero PubMed results, re-checked the day this section was written.
• And as the section above now records, persimmon tannin has met living skin in the published literature exactly once, in guinea pigs, measuring pigmentation.

So the honest scorecard is: the molecule is documented and independently measured; the mechanism by which a tannin might act on it is plausible and has analogues in protein chemistry; and the product claim is untested. Anyone who tells you the first fact settles the third is overselling, and anyone who uses the absence of the third to dismiss the first is overcorrecting.

There is a third question underneath both of these, and it is the one a shopper actually has to answer: whether the reviews, roundups and ratings being used to sell the bars are evidence of anything. That is a separate investigation, and we have written it up as is persimmon soap legit — the Amazon Vine channel, the FTC rule on company-controlled review sites, and the Consumer Reports verdict that does not exist.

One practical footnote, since the thread is full of people reporting that a bar did nothing for them. In the accounts we have read, the commonest reason is not that the chemistry failed — it is that the smell being judged was never 2-nonenal, or that the pillow and the collar were never washed during the trial. Those are eight separate, checkable things, and working through them is how you find out whether the question even applies to you.

“It’s been used in Japan for generations” is not the counter-argument either. It appears in the same threads from the other side, and long use is a reason to investigate something rather than a result. Traditional use tells you a product is tolerable and popular; it does not tell you what it does to a specific molecule. The same standard that rules out the marketing claim rules this in only as a hypothesis.

What would settle it. A trial that would move this page: people randomised to a persimmon tannin bar or an identical bar without the tannin, washing a defined area on a defined schedule, with 2-nonenal measured off the skin by one of the methods listed above — rather than asked about — and bedding controlled, because fabric holds enough of the compound to be measured off it. Nothing like that has been published. If it is, we will write it up here whichever way it goes, and the contact page is how to tell us about it.

Commonly confused with

Four mix-ups account for most of the bad citations we see, including in otherwise careful articles.

• 4-Hydroxy-2-nonenal (4-HNE) is a different molecule with a vast literature in Alzheimer’s, ferroptosis and oxidative-stress research. It is not the body-odor compound. A PubMed search that picks up 4-HNE papers will wildly overstate how much “nonenal research” exists — we caught one in our own search and excluded it.
• Diacetyl is a separate age-related skin volatile with a different age curve, peaking in the 30s (Kimura 2016).
• 3M3SH and thioalcohols are the bacterial underarm odor compounds, produced by Staphylococcus hominis acting on apocrine secretions (Minhas 2018). Different smell, different cause, different fix — the distinction we work through in perimenopause body odor, and the reason a rinse-off soap and a leave-on deodorant are not competing products, which we set out in persimmon soap vs Lume. It is also why the antimicrobial approaches readers ask about, hypochlorous acid among them, are aimed at this compound rather than at 2-nonenal.
• Cucumber aroma. (E)-2-nonenal is one of the dominant volatiles in cucumbers. Same molecule, which is exactly why the original paper described the smell as “greasy and grassy”. The molecule is far better characterised as an odorant in food science than in dermatology — it is a proposed chemical marker for rancidity in olive oil (Neugebauer 2020) and a named green off-flavour compound in soy drink (Nedele 2021) — which is why what nonenal smells like is answered better by flavour chemists than by this literature.

Who can actually smell it

Almost every practical question about this odor runs into a measurement problem that has nothing to do with chemistry: the person most likely to have it is among the least likely to detect it. That is not a saying, it has been counted.

Murphy and colleagues (2002), in JAMA, tested olfaction in 2,491 adults aged 53 to 97 in Beaver Dam, Wisconsin, using the San Diego Odor Identification Test alongside self-report. Impaired olfaction was present in 24.5% overall and in 62.5% of those aged 80 to 97, and it was almost twice as prevalent in men. The part that matters most here is the comparison between the test and the self-report: only 9.5% reported a problem, and in the oldest group self-report identified just 12% of affected women and 18% of affected men.

Three consequences follow, and they run through most of the rest of this site.

• Self-assessment is not evidence. “It’s working, I can’t smell it any more” and “there’s nothing there” are both statements that a large fraction of older adults cannot reliably make. Nor is the reverse conclusive — adaptation to a constant, familiar odor is a separate mechanism from impairment, which is why some people do smell themselves; we work through the distinction in can you smell your own body odor.
• Any study relying on self-rated odor in older participants inherits this. It is why the one thing Willems 2022 is often criticised for — measuring emission rather than asking whether anyone noticed — is arguably a strength, and why the self-rated scoring in the industry patent work we read for does persimmon soap work is a weaker endpoint than it looks.
• It reframes the family conversation. If most affected people over 80 do not know their sense of smell has changed, then someone who cannot smell a problem is not denying it — a point with practical consequences for telling an elderly parent they smell.

Murphy and colleagues were studying olfaction generally, not body odor, and nothing in the paper is about 2-nonenal. It is included here because it is the best-characterised constraint on how any of this research, and any product claim built on it, can be evaluated by the people it concerns.

The error runs the other way too, and that has not been measured against this molecule either. Readers in midlife report the opposite of decline — that everything arrives too strongly — and the question of whether a sharper nose or a changed one is behind it is a real and separately evidenced subject, which we set out in a heightened sense of smell in menopause. For this page the relevant fact is narrow: a title-and-abstract search pairing 2-nonenal with hyperosmia, osmophobia or odour sensitivity returns zero records. Nobody has tested whether the people most likely to report this smell are unusually good at detecting it.

And a measured belief is not a measured odour. Persistent conviction of emitting an offensive smell that others do not notice is now a named ICD-11 diagnosis, olfactory reference disorder, which we deal with at length in can you smell your own body odor. One finding from it belongs here, in an index about what has been measured. Croy and colleagues (2025), in Psychiatry Research, developed a screening questionnaire from the ICD-11 criteria and gave it, with mental-health and olfactory measures, to 279 participants. Scores related to anxiety, depression and somatic symptoms — and not to olfactory sensitivity or to attitudes about smell. It is a questionnaire-development study, not a prevalence estimate, and the authors are explicit that the aetiological model they propose is a hypothesis. But the dissociation is the point: how strongly someone believes they smell has been measured against how well they smell, and the two did not move together. On a page about a molecule nobody can detect at home, that is worth holding on to in both directions.

The social evidence, for once measured

Most writing about this smell is about the person who has it. One 2026 paper looked at what it does to everyone else.

Zhao and colleagues (2026) combined field measurement in 35 elderly solo dwellings in Fuyang, China with an experiment exposing 75 participants to standardised (E)-2-nonenal under three conditions. Higher odor significantly reduced visitors’ stated intention to return, with the effect concentrated in the step from no odor to low odor — the first detectable trace did most of the damage. A combined design package of ventilation plus an entrance buffer plus enclosed storage sustained higher intention than ventilation alone.

The authors are careful that the design cannot isolate which component did the work, and the behavioural effect was not matched by the physiological measures. But it is the first study we found putting a number on the social cost, and it supports something the cleaning threads say constantly: a faint smell is not a small problem, and ventilation alone is not the whole answer. We go through the practical version in old person smell in a house.

When to see a doctor

Corrections and reuse

This page exists to be cited and to be corrected. If you are writing about age-related body odor and want to quote it, please do. If we have missed a paper, misread a result, or a new study has landed, tell us through the contact page — we will correct it and say what changed and when.

We are not a neutral party. We sell one of the products in this category and the disclosure sits at the top of every page. The way we try to handle that is by being harder on the evidence for our own product than anyone else would be, which is why the shortest section on this page is the one about ours.

Last full re-check of the literature: 3 November 2026. Changes made on that date, and on the earlier re-checks of 29 September and 8 October, are listed under “How we built this index” above. First published 20 September 2026.

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