What Is CAS Registry Number?
The CAS Registry is maintained by the Chemical Abstracts Service (CAS), a division of the American Chemical Society (ACS). Since 1957, it has been the world’s most authoritative database of chemical substance information, covering compounds reported in scientific literature — with thousands of new substances added daily.
Each registered substance is assigned a unique CAS Registry Number (CAS RN) — the universal identifier recognized across nearly all chemical databases.
A CAS number is a numeric identifier (up to 10 digits) divided into three parts by hyphens:
The first part: up to 7 digits
The second part: 2 digits
The third part: 1 check digit
The check digit validates the authenticity and uniqueness of the CAS RN.
Example:
For water (H₂O), the CAS number is 7732-18-5. The check digit “5” is derived from a mathematical formula based on the preceding numbers.
Why Get or Search a CAS Number?
CAS numbers are critical in the global chemical industry as they provide a standardized way to identify substances across different regulatory frameworks. Many regulatory and trade processes require CAS numbers, including:
Customs Declarations: Ensuring accurate classification and compliance with import/export regulations.
Chemical Registration Programs: Required in global compliance schemes such as EU REACH, China’s New Chemical Substance Notification (MEE Order No. 12), and U.S. TSCA Inventory Listing.
International Chemical Trade: Facilitating precise identification of chemicals in cross-border transactions.
When Is a CAS Number Required or Searched?
While many common substances already have CAS numbers available in public databases, new or patented substances may require an official search or application through the CAS Registry. Relevant companies or researchers dealing with proprietary chemicals, novel compounds, or regulatory submissions often need to apply for a CAS number to ensure proper documentation and classification.
Which Substances Are Eligible for a CAS Number?
CAS recognizes six main categories of substances that can be assigned CAS numbers:
Note: Mixtures cannot be assigned a CAS number, but their individual components can. Substances excluded from CAS registration include general categories, materials, living organisms, or trade products — e.g., anilines, shampoo, pineapple, glass bottle, or silver compounds.
How to Get a CAS Number?
Information Required for CAS Application or Inquiry
To ensure accurate identification, CAS requires detailed information for each category:
Providing complete information helps CAS chemists identify substances efficiently and avoid costly supplementary requests.
Standard Process
Submit required documents
CAS review
Supplementary information (if needed)
Receive results
CAS issues invoice (usually within two weeks)
Applicant completes payment
Timeline
Standard processing: 10 working days
Expedited (for IES only): 3 working days
Additional information requests may extend the timeline.
What are the CAS Service Types?
CAS offers two standard services for number assignment or confirmation:
(1) Chemist Consultation (CC) Service
Available for all eligible substance types
Supports INN and USAN identification confirmation
Different substance category reviewed by different experienced CAS chemist
(2) Inventory Expert Service (IES)
Specific to substances subject to U.S. TSCA Inventory requirements (e.g., PMN submissions)
Not available for non-TSCA substances such as hydrates or genetically modified materials
For simpler lookups, CAS also offers Registry Lookup service, which allows quick confirmation of CAS names or CAS numbers for substances with known identifiers. If the input matches the CAS Registry, results are typically returned within 24 hours.
Data Privacy in CAS Applications
Confidentiality is a crucial aspect of CAS applications. The CAS Registry will not disclose private information such as company details, addresses, or product-related data without prior authorization. The American Chemical Society (ACS) ensures strict data protection, preventing any third party from accessing proprietary information.
REACH24H's CAS Registration and Search Services
Navigating CAS registration can be complicated, especially for new substances. Our expert compliance team provides a range of services to assist relevant companies in obtaining or verifying CAS numbers efficiently:
Chemical Identity Verification: Ensuring substance information is accurate and meets regulatory standards.
CAS Number Search & Application: Assisting in identifying existing CAS numbers or applying for new ones.
Regulatory Compliance Support: Guiding relevant companies through chemical registration processes worldwide.
Liaison with CAS Authorities: Managing communications and follow-ups to expedite the CAS number assignment process.
Contact us today to simplify your CAS registration needs and ensure your chemical substances are properly documented and identified for international trade and regulatory purposes.
FAQs
What information is included in the results of a CAS number application/search?
The results generally include the CAS Registry Number (CAS RN) and the CA Index Name (CAS Name).
If the substance already exists in the CAS Registry, CAS will provide the matching CAS RN. If no match is found, a new CAS RN will be assigned.
At the same time, the substance will be publicly added to the CAS REGISTRY database. If confidentiality is required, applicants may choose to request only a CA Index Name instead of a CAS RN.
Why is the official CA Index Name different from the substance name provided by the applicant?
The CA Index Name is assigned by CAS according to the standardized CA naming rules—each CAS RN corresponds to one unique, authoritative CA Index Name.
The name provided by the applicant may be based on IUPAC or other naming conventions and may be non-standard or contain errors.
Therefore, the applicant’s submitted name is used only as a reference during the application/search process, and the final name is determined by CAS.
