Glossary / Identifiers
CAS Registry Number
A CAS Registry Number is a unique numeric identifier assigned by the Chemical Abstracts Service, a division of the American Chemical Society, to a specific chemical substance. It is written as three parts separated by hyphens, and the last digit is a check digit.
Explanation
Chemical names are messy. One substance can have a systematic name, a common name, a trade name, and names in several languages. A CAS number sidesteps that by pointing to exactly one substance, so it is the safest way to be sure two documents are talking about the same material.
The number itself carries no meaning about structure or hazard. It is simply assigned in sequence as substances are registered. The final digit is calculated from the others so that typing errors can be caught.
On an SDS, CAS numbers are used to identify each ingredient listed in Section 3. Regulations also use them: lists such as CERCLA reportable quantities, Proposition 65 listings, and many exposure limits are keyed to CAS numbers.
A CAS number identifies a Substance, not a Mixture. A product that is a blend has no single CAS number, so you may find a number for each component instead. Salts, hydrates, and different forms of the same element can have different numbers, so check the full number rather than just the name.
Searching by CAS number is usually the most reliable way to find a chemical's records across databases.
What to do and watch for
- Use the CAS number, not just the name, when requesting an SDS or checking a regulatory list.
- Verify all three parts of the number; a single wrong digit points to a different substance or none.
- Remember a mixture will list component numbers rather than one number for the whole product.
Where it appears on an SDS
- Section 1: Identification. The product identifier may include a CAS number when the product is a single substance.
- Section 3: Composition / information on ingredients. The composition section lists the CAS number of each hazardous ingredient and often its concentration range.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.