Understanding CAS Numbers and Why They Matter in Chemical Sourcing
CAS Registry Numbers are the universal language of chemistry. Learn how to use them to find exactly the ingredient you need — every time.
If you've ever tried to source a chemical ingredient and struggled to match a supplier's trade name to what your formulation calls for, you've experienced the core problem that CAS numbers solve. A CAS Registry Number is the most reliable way to identify a chemical substance unambiguously — across languages, trade names, INCI names, and regions.
What Is a CAS Number?
CAS stands for Chemical Abstracts Service, a division of the American Chemical Society. Since 1965, CAS has assigned unique numerical identifiers to every substance in their registry — now exceeding 200 million entries. The format is three number groups separated by hyphens: [prefix]-[serial]-[check digit]. For example, water is 7732-18-5, and glycerine is 56-81-5.
The check digit (final single digit) is computed from the preceding numbers, which means any random string of numbers won't pass as a CAS number — helping to catch typos and errors.
Why Trade Names Aren't Enough
The same chemical can have dozens of names. Glycerine is also called glycerol, propane-1,2,3-triol, and 1,2,3-propanetriol. In personal care, it appears under its INCI name (Glycerin). Suppliers may use their own trade names: Croderol, Pricerine, Emery 912. These are all the same substance — CAS 56-81-5 — but without the CAS number, cross-referencing suppliers is unreliable.
How to Use CAS Numbers in Sourcing
- Search by CAS first: Most databases, including Chemizon, support CAS number search — use it to get an exact match rather than relying on name variants
- Cross-reference the COA: A Certificate of Analysis from a supplier should always list the CAS number. If it doesn't, request an updated version
- Verify before substituting: When considering an alternative ingredient, compare CAS numbers to confirm they are the same substance, not just a similar-sounding one
- REACH and regulatory databases: ECHA's REACH database is indexed by CAS number — looking up regulatory status requires the CAS number to get accurate results
CAS vs. INCI vs. EC Number
These identifiers serve different purposes and are often confused:
| Identifier | What It Is | Primary Use |
|---|---|---|
| CAS Number | Universal chemical identifier | General chemistry, sourcing, regulatory filings |
| INCI Name | Standardised cosmetic ingredient name | Required on EU/US cosmetic labels |
| EC Number | EU regulatory identifier (EINECS/ELINCS) | REACH compliance, EU import/export |
A single substance can have all three. When sourcing for cosmetics, you may need the INCI name for labelling, the CAS number for supplier identification, and the EC number for REACH compliance — three different lookups for the same ingredient.
Finding CAS Numbers
Reliable sources for CAS number lookup include the NIST WebBook, PubChem (US National Library of Medicine), ECHA's chemical inventory, and ingredient databases like Chemizon. Avoid relying solely on Wikipedia — while often accurate, it's not authoritative for regulatory purposes.
Chemizon Editorial
Published on May 28, 2026