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EU AllergenCAS 127-51-5

ALPHA-ISOMETHYL IONONE — EU Regulated Fragrance Allergen

Methyl-gamma-ionone

ALPHA-ISOMETHYL IONONE is included in this site's EU fragrance-allergen reference set. The general declaration threshold is above 0.001% in leave-on products or above 0.01% in rinse-off products, but any linked Annex II or III conditions also apply.

This page links ALPHA-ISOMETHYL IONONE to 1 annex record in the EU cosmetics dataset. Declared on the label when present above 0.001% in leave-on products or 0.01% in rinse-off products under EU Cosmetics Regulation 1223/2009 Annex III.

Leave-on products
> 0.001%
Label declaration required
Rinse-off products
> 0.01%
Label declaration required
Check your formula for this allergen All allergens View annex entries for this CAS

Regulatory status

INCI name

ALPHA-ISOMETHYL IONONE

CAS number

127-51-5

Synonyms

Methyl-gamma-ionone

Declaration requirement

Must be declared on the cosmetic product label when present above 0.001% in leave-on products or above 0.01% in rinse-off products.

Legal basis

EU Cosmetics Regulation 1223/2009, Annex III

Additional chemical sources

Search the same identity in independent official chemistry and hazard databases. These sources provide context and do not replace the EU labelling rule above.

ECHA CHEM

EU substance information and CLP classification where available.

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US EPA CompTox

EPA chemistry, exposure and toxicity data search.

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Annex records for ALPHA-ISOMETHYL IONONE

Why ALPHA-ISOMETHYL IONONE matters for EU labelling

ALPHA-ISOMETHYL IONONE has a dedicated fragrance-labelling reference page and currently links to 1 annex record. Regulation (EU) 2023/1545 also added 56 allergens and updated existing entries, so current Annex III evidence remains authoritative.

Declared on the label when present above 0.001% in leave-on products or 0.01% in rinse-off products under EU Cosmetics Regulation 1223/2009 Annex III.

Allergen declaration is a labelling obligation, not an automatic ban. If additional Annex II or Annex III conditions apply through the linked records above, those conditions must be checked separately from the label declaration thresholds.

Frequently asked questions

ALPHA-ISOMETHYL IONONE is included in the fragrance-allergen labelling reference. A labelling rule does not by itself establish that an ingredient is permitted: an Annex II prohibition or additional Annex III restriction may also apply. Check every linked current annex record above.

Declaration of ALPHA-ISOMETHYL IONONE is mandatory when the concentration exceeds 0.001% (10 ppm) in leave-on cosmetic products or 0.01% (100 ppm) in rinse-off products. Below these thresholds, label declaration is not required but may be made voluntarily.

The concentration threshold applies to the allergen in the finished product. When the allergen is contributed by a fragrance blend, the allergen content of the blend (provided by the fragrance supplier) must be multiplied by the percentage of blend used in the formula. If the calculated total allergen concentration exceeds the threshold, it must be declared on the label.

Use the INCI Checker to paste your ingredient list. It checks dedicated allergen references including ALPHA-ISOMETHYL IONONE and scans all Annex II–VI entries, including the expanded Annex III records introduced or updated under Regulation (EU) 2023/1545.
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CAS 127-51-5 identifies ALPHA-ISOMETHYL IONONE in the EU regulatory databases. The annex records linked above show all Annex II–VI entries that share this CAS number, including any additional restriction or prohibition conditions beyond the allergen labelling requirement.

Source note for ALPHA-ISOMETHYL IONONE

This page combines the EU allergen-labelling rule for ALPHA-ISOMETHYL IONONE with 1 linked Annex II–VI record drawn from the current local dataset.

Use this page to review labelling logic for ALPHA-ISOMETHYL IONONE, but verify any final compliance decision against the current official allergen rules, annex text and source files.

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Tools & next steps

Check your formula

Scan a full INCI list for ALPHA-ISOMETHYL IONONE, the other EU allergens and any linked annex restrictions.

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Allergen references

Browse the site's dedicated allergen references and continue to the complete current Annex III records from ALPHA-ISOMETHYL IONONE.

View all allergens

Calculate the threshold

Calculate the finished-product level of ALPHA-ISOMETHYL IONONE contributed by a fragrance or raw-material blend.

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Annex entries by CAS

View all EU annex records sharing CAS 127-51-5.

View CAS records