My database cannot settle the synthetic-versus-natural argument, because its two fields contradict each other

Someone started a thread on r/DIYfragrance after seeing a few influencers on Instagram recommending their preferred "non-toxic and safe" home fragrances:

"One influencer said that synthetic materials are what made products 'unsafe' and 'toxic'. Another one said they use essential oils to fragrance their home and they are good because they are natural (as if essential oils are not often more allergenic than 'synthetic' fragrance)."

Ninety-seven replies. Most agreed with them, and the back half turned into an ugly argument — a user describing severe reactions of her own was told by several commenters that her body "cannot tell chemical molecules apart".

We have already written Are naturals gentler (on sensitization rates) and The same name is not the same material (on batch variation). This article handles something else: the thread contains one claim specific enough to test, and the test turned out more interesting than the question.

The short version

• Someone in the thread said naturals will not last more than 24 hours on skin. I tested it, and the two relevant database fields give opposite answers.
• By the natural/synthetic field: the 500 materials labelled natural average 182.7 hours, against 97.7 hours for the 25 labelled synthetic. Naturals last longer.
• By the natural-occurrence field: the 728 materials not found in nature average 172.1 hours, against 136.1 for the 1,299 that occur naturally. Synthetics last longer.
• The two fields flatly contradict each other on 306 records — they read "not found in nature" in the occurrence field while being labelled "natural" in the other.
• So that claim cannot be settled with this data. And the thing more worth noticing is that the category itself is not a clean division in the data.
• The worst line in that thread was "your body literally cannot tell chemical molecules apart". That is false, and we have cited the receptor-level evidence. The reverse holds too: an unestablished mechanism does not mean the reaction is not real.

About a 9 minute read.

The testable claim

Late in the thread, someone describing nearly twenty years of making custom fragrances wrote:

"What people often forget when they say naturals have all kinds of chemicals, yada yada alike synthetics… naturals are not going to last on the skin for upwards of over 24 hours. Someone who has a migraine or asthma issues that is serious. Naturals offer more intimate wear that is less diffusive and has less high impact."

This is the most concrete claim in the whole thread, and its use is very practical: it is telling someone with severe reactions that naturals are therefore better for them. If it is wrong, that reader is getting false reassurance.

My database has a longevity field, so this is checkable.

First test: naturals last longer

The database's natural_synthetic field has three values. Taking records with a non-null longevity figure:

Class	Materials	Mean longevity	Share over 24 hours
Natural	500	182.7 hours	70.8%
Natural/synthetic	1,296	135.7 hours	60.2%
Synthetic	25	97.7 hours	56.0%

The direction is the reverse of the claim. Materials labelled natural last longer on average and cross 24 hours more often.

Hold the conclusion, though, because that synthetic group is 25 materials. Twenty-five samples cannot carry a comparison, and the reason it is so small is that most materials in this field are not labelled "synthetic" at all.

Second test: change the field and the answer flips

The database also has an occurrence field recording whether the molecule has been found in nature. That is closer to what people actually argue about. Re-running on it:

Class	Materials	Mean longevity	Share over 24 hours
Occurs in nature	1,299	136.1 hours	59.2%
Not found in nature	728	172.1 hours	72.7%

This time the ones nature does not make last longer.

Two fields, two directions, one question.

Why they disagree

Because the two fields classify the same materials inconsistently, and the inconsistency is large.

Across all 42,225 records:

natural_synthetic field	Records
natural	17,818
natural/synthetic	4,762
synthetic	836
blank	18,809

Meanwhile, 14,816 records say "not found in nature" in the occurrence field.

Fourteen thousand eight hundred and sixteen against eight hundred and thirty-six. If a molecule cannot be found in nature then it is synthetic — but only 836 are labelled that way.

Look at the overlap directly: of the 728 materials with a longevity record that say "not found in nature", 306 are labelled "natural" in the other field.

One record, where one field says it does not exist in nature and the other says it is natural.

This is not the database being wildly wrong; the two fields are about different things. natural_synthetic is mostly about how you can obtain it (many molecules can be extracted from plants and made in a factory), while the occurrence field is about whether it has been detected in nature. Those were never the same question.

But the people arguing think they are. That is where this whole argument comes apart — where the line falls depends on which question you asked, and most people have not made the question explicit.

So what about the 24 hours

Cannot be settled.

All I can say is this:

• Neither cut supports "naturals last a shorter time", and one of them points explicitly the other way;
• the synthetic group under one cut is 25 materials, which is too few;
• and under the other cut, the 728 not found in nature last longer (172.1 against 136.1).

If someone offers "naturals last a shorter time" as advice to a sensitive person, this data does not support it. It does not clearly refute it either — but reassurance without evidence and no reassurance are different things.

A reminder in passing: those longevity figures have a 400-hour ceiling, with 13.3% of materials piled at the top of the scale, and lasting on a blotter and being smellable on skin are different measurements.

The worst line in the thread

The back half of the thread is hard to read. A user described her situation in detail — a histamine-response condition, certain products causing nausea and respiratory problems within one to two hours, and no problems so far with the things she makes herself from essential oils and simple carriers.

A reply told her:

"And your body literally cannot tell chemical molecules apart."

That is false.

Bodies tell molecules apart through receptors. Two articles ago we cited Givaudan's 2024 work: on the human musk receptor OR5A2, a single amino acid substitution (P172L) cuts sensitivity around 50-fold, and people homozygous for that mutation have detection thresholds 40 to 60 times higher for that receptor's selective ligands. Individual differences have their own article too.

Your nose and someone else's can differ by two orders of magnitude on the same molecule. "Cannot tell molecules apart" fails on the literal words.

Another reply in the same exchange is worth copying:

"The amount of people that are pro-synthetic that gaslight people having real negative reactions to synthetic materials is insane."

But the other direction fails too

This article is not taking the "so synthetics are toxic" side. That conclusion is equally unsupported.

Steinemann, in the Journal of Occupational and Environmental Medicine in 2018, surveyed a nationally representative cross-sectional sample of 1,137 American adults in June 2016:

	Share
Report medically diagnosed multiple chemical sensitivities (MCS)	12.8%
Report chemical sensitivity	25.9%

Among those with MCS:

• 86.2% experience health problems, such as migraine headaches, when exposed to fragranced consumer products;
• 71.0% are asthmatic;
• 70.3% cannot access places that use fragranced products such as air fresheners;
• 60.7% lost workdays or a job in the past year due to fragranced products in the workplace.

The paper concludes that prevalence of diagnosed MCS has increased over 300%, and self-reported chemical sensitivity over 200%, in the past decade.

Those figures describe a large effect. Sixty percent losing work is not the scale of "imagining it".

On mechanism, Bensefa-Colas and Dupas, reviewing the field in La Revue du Praticien in 2014, are equally clear: idiopathic environmental intolerance is characterised by a variety of non-specific symptoms involving several organs within the same individual, attributed to exposure to chemical odours. Symptoms occur following exposure to agents generally regarded as harmless due to the low levels of exposure, and they do not answer to any definition of organic diseases. The lack of established etiology renders treatment difficult. Their recommendation is that practitioners recognise such disorders and assess the social and professional impact in order to improve patients' quality of life.

Put the two together and the honest statement is this: the reactions and the disability are real, measurable and widespread; the mechanism is not established, and it has not been attributed to the category "synthetic".

Steinemann's study is self-report, including the "medically diagnosed" item, which respondents reported themselves rather than being verified against records. Keep that in mind reading those percentages.

What to use instead of the rule

We gave one answer before; here is what this round adds.

One: look things up by molecule, not by category. Natural versus synthetic is not the unit of risk; the molecule is. Here is how to check IFRA's 263 standards.

Two: if you have clear reactions, record products and ingredients, not "natural" or "synthetic". The user in that thread was actually doing the right thing — her husband writes down the additives that consistently cause problems and buys around that list. That list is at the molecule level, which beats any category.

Three: do not offer "naturals last a shorter time" as reassurance to anyone. This data does not support it.

Four: treat the word "non-toxic" as carrying no information. Dose, route and finished-product concentration carry information. IFRA's percentages are of the finished product, which is a statement with content.

What this doesn't establish

The synthetic group is 25 materials. The first comparison is close to statistically meaningless; it is here because it points the opposite way from the second, and that contradiction is the point.

Longevity hours are not skin longevity. These are blotter records with a 400-hour ceiling, sourced principally from one person's observations in the 1990s. Using them to answer "how long does it last on skin" is several steps removed.

I did not test diffusiveness or impact. The claim's other two halves ("less diffusive", "less high impact") have no field I trust to test them — the strength field is a verbal grade rather than a measurement, and its resolution cannot even separate vanillin from ethyl vanillin.

Two fields disagreeing does not tell me which one is right. I cannot adjudicate between them from inside the database, so I have printed both and explained that they answer different questions.

Steinemann's figures are self-reported. A nationally representative sample is the study's strength; self-report is its limitation, and both belong in the sentence.

Bensefa-Colas is a review rather than primary research, and it is from 2014. Consensus in that field may have moved.

I cannot tell any individual why they react. The one thing this article can do is show that the natural-versus-synthetic category does not answer that question.

References

A. Steinemann, National Prevalence and Effects of Multiple Chemical Sensitivities, Journal of Occupational and Environmental Medicine, 60(3), e152–e156 (2018). PMID 29329146. doi:10.1097/JOM.0000000000001272

L. Bensefa-Colas, D. Dupas, Idiopathic environmental intolerance: 2 disabling entities to recognize, La Revue du Praticien, 64(3), 358–362 (2014). PMID 24851372

Related: Are naturals gentler, The same name is not the same material, Individual differences, Is this material still legal.