Why does CAS 91-56-5 appear in more than one EU cosmetic annex?

A substance identified by CAS 91-56-5 may appear in multiple EU cosmetic regulation annexes when it is subject to different conditions in different contexts — for example, restricted under Annex III with specific conditions, while also appearing in Annex IV as an approved colorant under separate entry conditions. Each entry must be reviewed individually.

How do I check if my formula contains a substance with CAS 91-56-5?

Use the INCI Checker on CosIng Checker with INCI names, CAS numbers or EC numbers. Paste CAS 91-56-5 to screen it directly, then review every linked annex record and supplier document.

CAS 1 record

CAS 91-56-5

Q: How do I use CAS 91-56-5 for compliance screening?

Cross-reference CAS 91-56-5 against your raw material specification sheets and CoA documents. When it appears in Annex II, verify absence. When it appears in Annex III, verify that concentration limits and product type conditions are met. All annex entries sharing this CAS number are listed on this page.

CAS 91-56-5 matches 1 EU annex record across Annex II–VI of Regulation 1223/2009.

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Chemical identity and properties

PubChem 2D chemical structure for CAS 91-56-5

CAS 91-56-5PubChem CID 7054

Isatin

Isatin is an indoledione that is the 2,3-diketo derivative of indole. It has a role as an EC 1.4.3.4 (monoamine oxidase) inhibitor and a plant metabolite. — ChEBI

IUPAC name: 1H-indole-2,3-dione

Molecular formula: C8H5NO2
Molecular weight: 147.13 g/mol
Exact mass: 147.032028402 Da
XLogP3: 0.8
Topological polar surface area: 46.2 Å²
Hydrogen-bond donors: 1
Hydrogen-bond acceptors: 2
Covalent units: 1
Defined stereocentres: 0

Also known as

INDOLE-2,3-DIONE2,3-Diketoindoline2,3-DioxoindolinePseudoisatinIsotinIsatic acid lactamIsatinic acid anhydrideo-Aminobenzoylformic anhydride

16 more reported names

2,3-Dioxo-2,3-dihydroindole2,3-dihydro-1H-indole-2,3-dioneCHEBI:27539NSC-926282X95S7M062,3 DioxoindolineRefChem:148910Indoline-2,3-dione2,3-IndolinedioneIsatineTribulin2,3-KetoindolineNSC 9262UNII-82X95S7M062,3-dihydroindole-2,3-dione5-21-10-00221 (Beilstein Handbook Reference)

Open full PubChem record PubChem annotations 3D structure image

External database identifiers

ChEBI:CHEBI:27539
ChEMBL:CHEMBL326294
EPA DTXSID:DTXSID3038694
PubMed:30926317
PubMed:24636345
PubMed:24316276
PubMed:24246760
PubMed:23295225
PubMed:23247010
PubMed:23103534
PubMed:23044749
PubMed:23028517
PubMed:23011183
PubMed:22969614
PubMed:22920713

Retrieved from NIH PubChem on 2026-09-02 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

Records for CAS 91-56-5

1 total

Annex

III

Entry

210

ISATIN

1H-Indole-2,3-Dione

Hair colorants can cause severe allergic reactions. Read and follow instructions. This product is not intended for use on persons under the age of 16. Temporary ‘black henna’ tattoos may increase your risk of allergy. D…

202-077-8

Max concentration

How CAS 91-56-5 is used on this site

CAS 91-56-5 is the Chemical Abstracts Service identifier used to pin this page to a specific substance. In the current dataset, 1 EU annex record shares this identifier, which helps you cross-check whether the same substance appears under one regulatory context or several.

Use this page when a supplier specification, SDS or raw-material dossier gives you CAS 91-56-5 and you need to see every linked Annex II–VI record in one place. The entry cards above are the quickest route to concentration limits, warnings, annex placement and product-type conditions.

Frequently asked questions

A substance identified by CAS 91-56-5 may appear in multiple EU cosmetic regulation annexes when it is subject to different conditions in different contexts. For example, a substance might be restricted under Annex III with specific conditions, and the same CAS might also appear in Annex IV as an approved colorant under separate entry conditions. Each entry must be reviewed individually.

Cross-reference the CAS number against your raw material specification sheets and CoA documents. When a CAS appears in Annex II, verify absence. When it appears in Annex III, verify that concentration limits and product type conditions are met in your formulation. All annex entries sharing this CAS number are listed above.

A CAS number is assigned by the Chemical Abstracts Service (USA) and is globally recognised. An EC number is a European Commission identifier from inventories such as EINECS, ELINCS or the NLP list. Both identifiers may appear in EU cosmetic annex entries. Some substances have both, some have only one, and some older entries may have neither.

The INCI Checker accepts ingredient names, CAS numbers and EC numbers. Check this CAS number directly, then verify the result against supplier specification sheets and every linked annex condition.

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