Short answer
A chemotype is a chemically distinct form of the same plant species: plants that look the same and share a botanical name but produce essential oils dominated by different constituents. Thyme, rosemary and basil are classic examples — a "thyme oil" may be dominated by thymol, by linalool or by other constituents depending on chemotype, and smells accordingly. For perfumers, the chemotype is part of a natural material's identity, alongside species, plant part, origin and extraction method. Record it, ask suppliers for it, and do not treat two oils with the same common name as interchangeable without checking.
Why chemotypes exist
A plant's essential oil is a mixture of many compounds. Genetics, climate, soil and growing conditions shift the proportions, and within some species distinct, stable forms occur in which one constituent dominates. Those forms are called chemotypes, abbreviated "ct." in product names: "Thymus vulgaris ct. linalool".
Chemotypes are different from:
- Different species or hybrids sold under one common name — lavender (Lavandula angustifolia) and lavandin (a hybrid) are different plants, not chemotypes.
- Different plant parts — leaf, flower, bark and fruit oils from one tree can differ completely.
- Different extraction methods — an essential oil, an absolute and a CO₂ extract of the same plant are different materials; see essential oils, absolutes and isolates.
- Normal lot-to-lot variation, which is smaller and continuous.
Examples perfumers meet
| Plant | Chemotypes often sold | Smell |
|---|---|---|
| Thyme (Thymus vulgaris) | ct. thymol; ct. linalool; others | Phenolic, medicinal (thymol) vs soft, floral-herbal (linalool) |
| Rosemary (Salvia rosmarinus, formerly Rosmarinus officinalis) | ct. cineole; ct. camphor; ct. verbenone | Fresh-eucalyptus vs camphoraceous vs softer, greener |
| Basil (Ocimum basilicum) | Linalool-rich; methyl chavicol-rich | Sweet-floral vs anise-like |
| Camphor tree (Cinnamomum camphora) | ct. linalool (sold as ho wood or ho leaf); camphor-rich forms | Floral-woody linalool vs camphoraceous |
The exact constituents and their ranges come from the supplier's certificate of analysis, which for naturals often includes a gas chromatography profile of the main components.
Why it matters in a formula
- Odor. Two chemotypes of the same plant can smell as different as two different plants. Replacing one with the other changes the formula.
- Allergens and restrictions. Constituent profiles drive allergen declarations and some restrictions. A linalool chemotype contributes far more linalool — an EU-listed allergen — than a thymol one. Calculations for declarations use the constituents of the actual oil you use; see EU fragrance allergen labelling.
- Supply. A supplier switching chemotype, or simply not specifying one, can change your product without the name changing.
What to record
- Botanical name, with chemotype where one applies.
- Plant part and extraction method.
- Origin (country or region), where the supplier gives it.
- Main constituents from the lot's certificate of analysis, especially allergens and restricted constituents.
- Supplier, product code and lot.
- Your own odor description of that lot.
These fields belong in the material's record so that every formula using it inherits the same identity. The full list of material fields is in perfume raw material documentation. In RUŌOD Lab, a material carries a botanical name and a CAS number among its standard fields, and you can add a custom field for chemotype if you track it.
Buying and switching
- When you first buy an oil whose species has chemotypes, ask which one it is. If the supplier cannot say, ask for the constituent profile.
- When reordering, check that the chemotype and main constituents match the previous lot.
- If you change supplier, treat it as a material change: compare odor and constituent profiles, and re-evaluate formulas that rely on it. Documenting raw material supplier changes covers the record.
Note also that CAS numbers for essential oils usually identify the botanical source broadly, not the chemotype, so a CAS number alone does not settle the question.
Frequently asked questions
Are chemotypes the same as "grades"?
No. A grade is a supplier's commercial classification, which may reflect origin, processing or quality. A chemotype is a botanical-chemical distinction. A supplier may sell several grades of one chemotype.
Do chemotypes matter for synthetic materials?
No — they are a property of plants. Synthetic materials vary in purity and isomer ratio instead, which you record from their specifications. See natural vs synthetic fragrance materials.
Written and reviewed by the RUŌOD Lab team. This article is general education about perfume formulation and record-keeping; it is not legal, regulatory or safety advice, and the examples are illustrations, not validated commercial formulas. How we write and check these guides.