CAS, EINECS, and EC Numbers: Which One a Filing Wants

Pull up three different supplier safety data sheets for the same raw material and you'll probably find three different numbers sitting next to the ingredient name. One's a CAS number. One might be labeled EINECS. Another says EC. They look similar, seven or so digits with dashes, and it's genuinely easy to grab the wrong one when you're filling out a notification at 11pm.

CAS numbers, the one you'll use most

CAS stands for Chemical Abstracts Service, and a CAS registry number is a unique identifier assigned to a specific chemical substance, independent of what regulatory region you're in. Propylene glycol, for example, carries CAS 57-55-6 everywhere in the world, regardless of which country's cosmetic authority you're filing with. This is the identifier you'll most often be asked to reference for single, well-defined chemical substances.

A few quirks worth knowing:

• Some substances have more than one valid CAS number, often because of historical registration quirks or because a substance was registered separately before someone recognized it was chemically identical to something already registered.
• Complex natural substances, like whole botanical extracts, sometimes don't have a clean CAS number at all, since they're mixtures rather than single defined compounds. That's normal, not an error on your part.
• Trade names never map directly to a CAS number without going through the actual chemical identity first. "Vitamin E" needs to become "Tocopherol" before you can attach CAS 59-02-9 to it, for example.

EINECS and EC numbers, the European-context identifiers

EINECS stands for the European Inventory of Existing Commercial Chemical Substances, a list that was compiled to catalog substances already on the European market at the time it was created. An EC number (sometimes called an EINECS number when it comes from that specific inventory) is the identifier tied to that European chemical inventory system, used heavily in EU chemical and cosmetic regulatory contexts.

The practical difference for a maker: EC/EINECS numbers are the identifier you'll encounter and need when working within EU regulatory paperwork, particularly around the Cosmetic Product Safety Report and safety assessor documentation required under the EU's cosmetic framework. If you're filing exclusively in Canada, you're far less likely to need this number at all, since the Canadian system is built around INCI names with CAS numbers as the common cross-reference.

A side-by-side to keep straight

Identifier	What it identifies	Where you'll actually need it	Format example pattern
INCI name	Standardized cosmetic ingredient name	Every market's ingredient declaration	Butyrospermum Parkii Butter
CAS number	Unique chemical substance registry ID	Cross-referencing composition, most SDS sections 1-3, general international use	57-55-6
EC / EINECS number	EU chemical inventory identifier	EU-specific regulatory and safety assessor documentation	200-338-0 (example format)

Where mistakes actually happen

The confusion I see most isn't makers not knowing these are different systems. It's pulling the wrong number off a supplier document because the SDS lists both without clearly labeling which is which, or because a supplier's regional office generated documentation formatted for their home market's expectations rather than yours.

Before you paste any identifier into a notification form:

1. Check the label on the number itself in your source document. Reputable safety data sheets label section 3 (composition) clearly, but not all suppliers are equally careful, especially smaller or overseas suppliers.
2. Cross-check against the INCI name, not just the number. If you know the ingredient's INCI name, you can independently verify whether the CAS number attached to it looks right, since CAS numbers for well-known ingredients are consistent and searchable.
3. Don't assume an EC number will work where a CAS number is expected, or vice versa. They come from different systems built for different regulatory contexts, and a reviewer checking your filing against a restricted substance list is going to be looking for the identifier that list is actually built around.

Why this matters more as you expand markets

If you're filing only in Canada right now, CAS numbers alongside INCI names are your main reference point, and EC numbers are largely irrelevant to that specific filing. But the moment you start planning an EU notification, EC/EINECS numbers become directly relevant to your Product Information File and safety assessor's work, so it's worth starting to track both identifiers in your formulation records now if a future EU launch is even a possibility, rather than reconstructing that research later under time pressure.

This is one of the quieter but genuinely time-consuming parts of expanding into new markets, and it's exactly the kind of ingredient identity work Cosmetic Comply is built around. It maps each ingredient to its correct INCI name and CAS number, keeps that data structured so it's ready to carry forward as you add markets, and flags anything ambiguous before it becomes a filing problem.