Where to Find the CAS Number on a Safety Data Sheet

You have got a sixteen-page PDF from your supplier and someone asked you for a CAS number. Do not read the whole document. There is exactly one section you need, and it is always in the same place.

Section 3 is where you look, every time

A safety data sheet follows a standardized 16-section format, and this is one of the genuinely useful things about SDS documents: no matter which supplier sent it, no matter which country they are based in, composition information lives in Section 3, titled something like "Composition/Information on Ingredients." Skip past Section 1 (identification) and Section 2 (hazard identification) and go straight there.

Section 3 typically lists, for each hazardous or notable component:

• The chemical name or common name
• The CAS number
• The concentration or concentration range in the product
• Sometimes an EC number (a European chemical identifier) alongside the CAS number

If you open an SDS and cannot find CAS numbers anywhere, check that you are looking at Section 3 specifically and not a different section that mentions the same ingredient in passing, like Section 8 (exposure controls) which sometimes references ingredients without repeating their CAS numbers.

Why CAS numbers do not automatically become your INCI list

Here is where makers sometimes trip up. A CAS number is a unique identifier for a specific chemical substance, not a naming system built for cosmetic labeling. INCI is the naming system built specifically for that purpose. The two serve different jobs, and Section 3 of an SDS usually shows you both the chemical name (which may or may not match INCI wording) and the CAS number side by side.

Your job is to make sure that whatever chemical name and CAS number combination the SDS gives you correctly maps to the correct INCI name for your filing. Sometimes the SDS chemical name and the INCI name are close enough to be obviously the same thing. Sometimes they are not, especially for raw materials sold under an industrial or generic chemical name that differs from cosmetic naming convention.

When an ingredient has more than one CAS number

Some substances legitimately have multiple CAS numbers, often because the substance can be produced by different processes that technically register as distinct entries, or because an older number was superseded by a newer one but both remain in circulation. If your supplier's SDS shows a CAS number that does not match the number you find elsewhere for what looks like the same INCI ingredient, this is often the explanation rather than an error. Note both numbers in your records and keep the supplier's documentation as the reference for which one applies to their specific material.

When there is no CAS number at all

Some ingredients, particularly botanical extracts, essential oils, and other complex natural materials, genuinely do not have a single CAS number, because they are mixtures of many constituent chemicals rather than one defined substance. An SDS for a plant extract may list the extract itself with no CAS number, or may list CAS numbers only for specific known constituents within it (like limonene within an essential oil) rather than for the extract as a whole. This is expected and not a sign of a bad or incomplete SDS. Your notification will typically use the INCI name for the botanical in these cases, since that is what the naming system was built to handle.

A quick reference for what you are looking for

SDS section	What is inside	Relevant to your filing?
Section 1	Product and supplier identification	Confirms you have the right document
Section 2	Hazard classification	Background safety context
Section 3	Composition, CAS numbers, concentrations	Yes, this is your target
Section 9	Physical and chemical properties	Sometimes useful for formulation, not for CAS lookup
Section 16	Other information, revision date	Confirms the SDS is current

Keep the SDS itself, not just the number you copied

When you pull a CAS number for your records, keep the source SDS on file too, along with its revision date. Suppliers update SDS documents periodically, and if a formula or concentration range changes, you want to be working from the current version rather than one you saved two years ago.

Cosmetic Comply's ingredient matching is built to take exactly this kind of supplier documentation, an SDS, a spec sheet, a trade name, and resolve it to the correct INCI name and CAS number for your filing, flagging the cases where an extract genuinely has no single CAS number rather than forcing a number that does not really apply.