A CAS number, short for Chemical Abstracts Service Registry Number, is a unique numerical identifier assigned to every chemical substance that has been documented in the scientific literature. Think of it as a universal ID card for chemicals: no matter what name a substance goes by in different countries, languages, or industries, its CAS number stays the same.
Who Assigns CAS Numbers?
CAS numbers are assigned by the Chemical Abstracts Service, a division of the American Chemical Society. The CAS Registry is the world’s largest database of chemical substance information, growing by thousands of newly registered substances every day and covering everything from simple elements to complex polymers, biological molecules, and mixtures.
What Does a CAS Number Look Like?
CAS numbers follow a consistent format: three groups of numbers separated by hyphens, with the last group always being a single check digit.
| Substance | CAS Number |
| Water | 7732-18-5 |
| Ethanol | 64-17-5 |
The numbers themselves don’t encode any chemical information. They’re sequential registry identifiers, which means two substances with similar structures or names can have completely unrelated CAS numbers, and there’s no way to infer a substance’s properties from the number itself.
Why Do CAS Numbers Matter for Safety Data Sheets?
CAS numbers play an important role in Safety Data Sheets. Section 3 of an SDS, Composition and Information on Ingredients, typically lists the CAS number for each of a product’s components. This makes it possible for safety professionals, emergency responders, and regulatory agencies to identify the substances present in a product quickly and unambiguously, rather than relying on a name that might not match what’s on file.
When a worker or first responder needs to look up hazard information during an emergency, searching by CAS number is far more reliable than searching by trade name or common name, both of which can vary widely across manufacturers, industries, and regions. The same underlying chemical can appear under a dozen different product names, but it only ever has one CAS number.
How Are CAS Numbers Used in Regulatory Compliance?
CAS numbers are widely used in chemical regulations worldwide. Regulatory lists, from OSHA’s Hazard Communication Standard to REACH in the EU and TSCA in the U.S., frequently reference substances by their CAS numbers rather than by name. If an SDS authoring process involves verifying regulatory status or checking ingredient-level compliance, accurate CAS numbers are essential to getting that check right the first time.
What Happens When CAS Numbers Are Wrong on an SDS?
Errors in CAS numbers on SDSs can lead to a chain of downstream problems:
- Misidentification of substances, which can cause a reviewer or responder to reference the wrong hazard data entirely
- Incorrect hazard classifications, since classification tools and regulatory lookups depend on matching the correct CAS number to the correct substance
- Compliance violations, particularly when a regulatory list check is performed against the wrong CAS number and misses a restricted or reportable substance
This is one reason purpose-built SDS authoring software, which draws on verified ingredient databases rather than manually re-entered data, is generally more reliable than manual authoring approaches. A single mistyped digit in a CAS number can point to an entirely different substance, and that kind of error is easy to introduce by hand and hard to catch during a manual review.
How Does SDS Authoring Software Reduce CAS Number Errors?
SDS authoring software reduces CAS number errors by pulling ingredient data directly from a verified database instead of relying on manual entry for every SDS. When an author selects an ingredient from a validated library, the correct CAS number, regulatory status, and classification data come with it, which removes the opportunity for a transcription error to reach the finished document.
TotalSDS Author uses a private, comprehensive ingredient library with verified CAS data, so SDSs are built on accurate ingredient identification from the start rather than depending on whoever is authoring the document to look up and re-enter each CAS number correctly. Once an SDS is finalized, SDS Manager keeps that verified ingredient data attached to the document across every site where it’s stored and accessed.
Key Takeaways
- A CAS number is a unique, permanent identifier assigned to a chemical substance, regardless of what trade or common name it’s sold under.
- CAS numbers follow a three-group, hyphen-separated format ending in a single check digit, and the digits themselves carry no chemical meaning.
- Section 3 of an SDS typically lists CAS numbers for each ingredient, which supports fast, unambiguous identification during audits and emergencies.
- Regulatory frameworks including OSHA HazCom, REACH, and TSCA reference substances by CAS number, making accuracy essential for compliance checks.
- Errors in CAS numbers can cause misidentification, incorrect classifications, and compliance violations, which is why verified ingredient databases are more reliable than manual entry.
Frequently Asked Questions About CAS Numbers
What is a CAS number used for? A CAS number uniquely identifies a chemical substance regardless of its trade name, common name, or the language it’s referenced in, which makes it the standard way to identify substances on Safety Data Sheets, regulatory lists, and emergency response references.
Who assigns CAS numbers? CAS numbers are assigned by the Chemical Abstracts Service, a division of the American Chemical Society, which maintains the CAS Registry as the world’s largest database of chemical substance information.
Does a CAS number tell you anything about a chemical’s properties? No. CAS numbers are sequential registry identifiers with no built-in chemical meaning. They exist purely to provide a unique reference, not to describe a substance’s structure, hazards, or properties.
Where do CAS numbers appear on a Safety Data Sheet? CAS numbers typically appear in Section 3 (Composition and Information on Ingredients), listed alongside each hazardous ingredient in the mixture.
What happens if a CAS number is incorrect on an SDS? An incorrect CAS number can lead to misidentifying a substance, applying the wrong hazard classification, or missing a regulatory restriction that would have applied to the correct substance, any of which can create compliance risk.
See How Verified CAS Data Improves SDS Accuracy
Manually re-entering CAS numbers for every ingredient on every SDS creates room for the kind of transcription error that leads to misclassification or a missed regulatory flag. TotalSDS Author uses a comprehensive ingredient library with verified CAS data, so SDSs are accurate from the start rather than dependent on manual lookups.
See how SDS Author handles ingredient-level accuracy, or explore SDS Manager to see how that verified data stays attached to your SDS library across every site.
