Safety · 5
"Synthetics give me headaches, so I only use naturals" — that split does not predict risk
· 24 min read
Someone said chemicals give them headaches and nausea, so they stick to naturals. The data says otherwise: across 18,832 European patch test patients, the highest-scoring fragrance marker is Myroxylon pereirae at 6.5%, a natural resin. In a German study of 10,930 patients, ylang ylang oil topped twelve essential oils at 3.9%. And among IFRA-regulated materials, naturals are more often banned outright than restricted. Our own database cannot settle the question, which is worth saying too.
Someone posted a formula to r/DIYfragrance for critique, opening with their stance: I'm a beginner and I'm deliberately sticking to naturals, because a lot of the chemicals give me headaches and nausea. Eighty-nine replies.
Elsewhere in the same community, someone found a large patch of oakmoss on a forest path in the French mountains and asked how to extract an absolute from it, noting specifically that they planned to make candles because that use is not IFRA restricted.
The pair is instructive. The second person knew to check the restriction. The first was using a shortcut rule: natural means safer.
That rule does not predict risk. Here is the data.
The short version
- Across 18,832 European patch test patients in 2021–2022, the highest-scoring fragrance marker is Myroxylon pereirae at 6.5% — a natural resin, edging out fragrance mix I at 6.39%.
- A German study of 10,930 patients tested twelve essential oils; 8.3% reacted to at least one, with ylang ylang oil highest at 3.9%.
- Of the 263 entries on the IFRA 51st Amendment index, 26 are recognisably naturals by name, and 11 of those 26 are outright prohibitions (42%). Among the other 237 entries, the prohibition rate is 30%.
- Our own database cannot answer this question. Of 17,002 materials carrying a natural/synthetic tag, only 367 have any GHS hazard data, and among the 637 tagged synthetic, not one does.
About a 9 minute read.
The highest-scoring marker is a natural
Start with the largest dataset.
The 2026 joint report by Uter and colleagues covers patch testing across 59 departments in 14 European countries during 2021 and 2022, totalling 18,832 patients. The two fragrance-related markers come out nearly level:
| Allergen | Positivity (95% CI) |
|---|---|
| Nickel | 18.85% (18.29–19.43) |
| Myroxylon pereirae (Peru balsam) | 6.5% (6.15–6.87) |
| Fragrance mix I | 6.39% (6.04–6.76) |
| MCI/MI preservative | 5.52% (5.11–5.96) |
| Propolis | 5.47% (5.12–5.84) |
Myroxylon pereirae is a resin from a Central American tree. It is a natural, and it stands second in the entire baseline series, behind only nickel.
Propolis in fifth place is a natural too.
Read the table fairly: Peru balsam functions in patch testing as a marker for fragrances and balsamics, so part of its score comes from cross-reactions rather than from that one material harming that many people. Even so, its position makes the point — if natural were a synonym for safe, it would not be sitting second.
Ten thousand people, twelve oils
The more direct evidence is Geier and colleagues, publishing in Contact Dermatitis in 2022 using data from the German IVDK dermatology network for 2010 to 2019.
10,930 dermatitis patients were patch tested in an aimed manner with twelve essential oils, and 908 (8.3%) reacted to at least one.
Six exceeded 1%:
| Essential oil | Positivity |
|---|---|
| Ylang ylang (I + II) oil | 3.9% |
| Lemongrass oil | 2.6% |
| Jasmine absolute | 1.8% |
| Sandalwood oil | 1.8% |
| Clove oil | 1.6% |
| Neroli oil | 1.1% |
Concomitant reactions between oils, and between oils and fragrances, were frequent. Among the oil-positive patients, the authors found women, leg dermatitis patients, people aged 40 and over, and masseurs and cosmeticians over-represented.
The authors' own conclusion is restrained: sensitisation to essential oils occurs, albeit infrequently in most cases, and the elevated risk sits with occupationally exposed groups such as masseurs and cosmeticians.
That restraint is worth copying. The study does not say essential oils are dangerous. It says essential oils are not exempt for being essential oils. And 8.3% describes a dermatology clinic population that already had symptoms.
Naturals on the IFRA list get banned rather than limited
A third angle comes from the regulatory list itself.
The IFRA 51st Amendment index I pulled for the previous piece holds 263 material entries. Sorting by name keywords (oil, absolute, extract, resinoid, balsam, moss and similar) gives 26 natural entries, 10% of the list.
The difference is in what kind of standard they get:
| Entries | Prohibition | Restriction or specification | |
|---|---|---|---|
| Recognisably natural by name | 26 | 11 (42%) | 15 |
| The rest (mostly single molecules) | 237 | 72 (30%) | 165 |
The eleven prohibited naturals include alantroot oil, birch wood pyrolysate, boldo oil, cade oil, chenopodium oil, costus root oil, absolute and concrete, fig leaf absolute, massoia bark oil, santolina oil, savin oil, and tagetes oil and absolute.
Take care not to over-read this. Those 263 entries are the materials IFRA decided needed managing, not a random sample of all materials, and my natural/synthetic split is a name match that will both misfire and miss. So these figures cannot support "naturals are more dangerous".
What they do support is narrower and sturdier: among materials that got regulated, naturals skew toward "don't use this at all" rather than "use less of it". The likely reason is that a single molecule can be controlled with a limit, while a natural is a mixture of hundreds; when no single component can be held responsible, prohibition is the remaining tool.
Incidentally, the oakmoss forager did their homework correctly — oakmoss is on the list, and it is restricted rather than prohibited.
Our own database can't answer it
Writing this, I wanted a neater analysis: take the GHS hazard classification for every material in the database and compare the rates between naturals and synthetics.
Here is what came back:
| Tag | Materials | With GHS data |
|---|---|---|
| natural | 11,845 | 31 (0.3%) |
| natural/synthetic | 4,520 | 336 (7.4%) |
| synthetic | 637 | 0 |
Of the 637 materials tagged synthetic, not one has the hazard field filled in. Comparing hazard rates across coverage like that measures whose records got completed, not who is safer.
The result is worth publishing because it is the standard failure of ingredient catalogues: hazard fields are filled in selectively, and the gaps are not random. Those three tags also do not mean "this jar was extracted or synthesised" — they mean "is this molecule found in nature", which is a different question again, and the eucalyptus piece covers another face of the same confusion.
Next time someone compares naturals and synthetics using catalogue fields, ask first whether both groups were filled in at the same rate.
What about the headaches
The poster described headaches and nausea, not a rash. Those are different things.
Everything above measures contact allergy — patch testing measures an immune response to skin contact. Headache and nausea belong to a different category of response with different mechanisms, and in this round of searching I found no study able to answer whether synthetics cause headaches more readily than naturals.
So the honest answer is: I don't know, and I did not find data that would settle it.
The more useful move is to change the question. Rather than asking natural or synthetic, record which material, at what concentration, in what situation made you feel unwell. That record is actionable and a category label is not — because the natural oil you bought is itself a mixture of hundreds of molecules, which makes "naturals give me headaches" exactly as unlocated as "synthetics give me headaches".
What to use instead of that rule
Look at the material, not the category. Every material has its own record: IFRA limits, GHS classification, patch test positivity. Is this material still legal has the lookup procedure.
Look at concentration. This is the one variable that works on both sides. Citrus phototoxicity involves naturals, hydroxycitronellal is a synthetic, and the handling is identical: find the limit for your product category and stay under it.
Look at oxidation. This one matters more for naturals. Linalool, geraniol and citral share the pattern of being mild when pure and sensitising when oxidised, and natural oils contain these components by default, so an ageing bottle drifts upward in sensitising potential. Decant, date, keep a reference.
The one thing the natural/synthetic line reliably predicts is batch consistency, and the direction does not favour naturals: keep the botanical name and change origin, plant part or year, and the ratios move with them.
What this doesn't establish
Patch test populations are not the general population. Both studies drew on patients already symptomatic enough to be referred. Neither 6.5% nor 8.3% is a prevalence.
The IFRA comparison is internal to the list. Those 263 entries are materials selected for regulation, not a sample of materials in general. The natural/synthetic split is a keyword match that will misclassify some single molecules and miss naturals whose names lack those words.
Peru balsam's high score includes cross-reactivity. Its role in the baseline series is as a marker, so the figure cannot be charged entirely to that one material.
This does not answer the headache question. I did not find the data, and guessing would not improve the article.
References
J. Geier et al., Contact sensitization to essential oils: IVDK data of the years 2010-2019, Contact Dermatitis, 87(1), 71–80 (2022). PMID 35417610. doi:10.1111/cod.14126
W. Uter et al., Patch Test Results With the European Baseline Series, 2021/2022 — Joint European Results of the ESSCA and the EBS Working Groups of the ESCD, and the GEIDAC, Contact Dermatitis, 95(1), 17–32 (2026). PMID 41819607. doi:10.1111/cod.70134
IFRA, Index of IFRA Standards – 51st Amendment (notified 2023-06-30). Checked 2026-08-27.
Related: How risky is DIY perfumery, Citrus phototoxicity, Eucalyptus globulus oil.