In short
alpha-Isomethyl ionone is a synthetic ionone with a soft, powdery violet-orris note. It is one of the most widely used materials for powdery, cosmetic florals.
What alpha-Isomethyl Ionone smells like
Alpha-isomethyl ionone is a powdery, velvety violet-orris with a soft woody side. BASF describes its Methylionone 70, of which it is the main component, as floral, velvety, violet, orris, a bit woody and fruity; a supplier as powdery — orris, violet, and also tobacco and wood. It is stable in most products including soap, lasts well, and is one of the 26 fragrance allergens individually named in EU cosmetics law.
- Leading note
- Powdery violet-orris
- Clear facets
- Velvety
- Supporting facets
- Woody
- Faint facets
- Tobacco, fruity
- Character
- Powdery, velvety, soft, stable
What makes alpha-Isomethyl Ionone distinctive
Orris rather than violet: the methylated ionone is more velvety and powdery, closer to iris root, and less fruity than the plain ionones.
How alpha-Isomethyl Ionone is used
Used very widely for powdery violet-orris effects in fine fragrance, cosmetics and soap.
Typical role: blender (smooths the joins between other materials).
How alpha-Isomethyl Ionone differs from similar materials
- alpha-Ionone
- Alpha-ionone is sweeter and fruitier violet; alpha-isomethyl ionone is more orris-like, velvety and powdery.
- Koavone
- Suppliers present Koavone as a modern methyl-ionone replacement, woodier and more ambery, with a toffee facet. (compared directly by a cited source)
An asterisk marks a difference that a cited source states directly. The others compare the published descriptions of each material. Smell varies with grade, supplier and dilution; compare them side by side on blotters before substituting one for another.
Formulation considerations
A declarable allergen; IFRA lists a Standard for methyl ionones.
Identity and classification
- Type
- Aroma chemical
- Origin
- Synthetic
- Odour family
- Powdery / Floral
- Note position
- Heart note
- Physical form at room temperature
- Liquid
- CAS number
- 127-51-5
- Molecular formula
- C14H22O
- Molecular weight
- 206.32 g/mol
- IUPAC name
- (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one
The CAS number, formula and molecular weight are taken from PubChem compound 5372174, whose own record lists this CAS number; checked 19 October 2026.
Safety and compliance
The IFRA Standards Library lists a Standard covering alpha-Isomethyl Ionone:
- "Methyl ionone, mixed isomers" — type not stated in the library listing, 49th Amendment, published 2020-01
Limits differ by product category and are set out in the Standard itself; this page does not reproduce them. The list above reflects the library as read on 19 October 2026.
alpha-Isomethyl Ionone is one of the 26 fragrance allergens listed individually in Annex III of the EU Cosmetics Regulation (label name: Alpha-isomethyl ionone), which must be named on cosmetic labels above 0.001% in leave-on and 0.01% in rinse-off products. Regulation (EU) 2023/1545 extended the list; see the fragrance allergens list.
Hazard classification of the neat substance, as PubChem summarises it, read 26 October 2026. Companies notifying the ECHA C&L Inventory classify it (1,992 reports): H317 may cause an allergic skin reaction (88.6% of reports); H411 toxic to aquatic life with long lasting effects (87.7% of reports); H315 causes skin irritation (78.1% of reports); H319 causes serious eye irritation (70.7% of reports); H412 harmful to aquatic life with long lasting effects (10.2% of reports). 37 of the reports find it does not meet the hazard criteria. A skin sensitiser classification concerns handling the neat material and the dose in a finished product; the IFRA Standards, where they apply, set the limits. Unless it is harmonised, this is the notifiers' own classification, not a binding one.
This page is general information, not a safety assessment or a specification. Confirm identity, composition, IFRA status and allergen content from your supplier's documents for the lot you hold.
Materials it works with
-
beta-Ionone
Aroma chemical · Powdery / Woody — violet, woody, fruity, raspberry
-
alpha-Irone
Aroma chemical · Powdery / Woody — orris, powdery, woody, violet
-
Orris Butter (Orris Concrete)
Concrete · Powdery / Woody — powdery, iris, woody, buttery
-
Heliotropin
Aroma chemical · Powdery / Gourmand — powdery, almond, vanilla, floral
alpha-Isomethyl Ionone is also suggested as a partner on the pages for Aldehyde C-12 Lauric (Dodecanal), Dihydro Gamma Ionone, Iralia Total, Methyl Beta Ionone, Orris Givco and Vertenex.
Used in formulas and accords
Used in 35 published formulas
alpha-Isomethyl Ionone is an ingredient in 19 perfume formulas, 13 accords and 3 bases in the Formula & Accord Library.
Community formulas
RUŌOD House Originals
Original compositions by RUŌOD House.
Further reading
Questions about alpha-Isomethyl Ionone
Is alpha-Isomethyl Ionone natural or synthetic?
alpha-Isomethyl Ionone is synthetic — it is made by chemical synthesis.
What is the CAS number of alpha-Isomethyl Ionone?
127-51-5. It was checked against PubChem on 19 October 2026.
Which published formulas use alpha-Isomethyl Ionone?
alpha-Isomethyl Ionone is used in 35 published formulas in the RUŌOD Lab Formula & Accord Library, including Anise Ink, Carnation Accord and Champagne Accord. Each is listed with a link under "Used in formulas and accords" on this page.
Is alpha-Isomethyl Ionone covered by an IFRA Standard?
Yes. The IFRA Standards Library lists a Standard covering it: "Methyl ionone, mixed isomers" — type not stated in the library listing, 49th Amendment. The limits depend on the product category; read the Standard itself before formulating.
Sources
- PubChem — compound 5372174, checked 19 October 2026.
- PubChem — GHS classification (the ECHA C&L Inventory notifications and any harmonised EU entry), read 26 October 2026.
- IFRA — Standards Library, read 19 October 2026.
- EUR-Lex — Regulation (EC) No 1223/2009, Annex III.
- BASF Aroma Ingredients — Methylionone 70 — manufacturer's description.
- The Good Scents Company — alpha-isomethyl ionone — odour database.
- Scentspiracy — Methyl Ionone Gamma A — distributor's description.
- Olfactory profile: the RUŌOD Lab team's synthesis of the published descriptions above, reviewed 20 October 2026. Evidence: several independent published descriptions, which agree. Classification and the short description: revision 1. Descriptions of odour are judgement, not measurement.