CAS numbers in perfumery: what they mean and why the same CAS does not guarantee the same smell

CAS numbers appear frequently in technical data sheets and product pages for perfumery raw materials. They are among the most useful pieces of information for identifying a substance, but they are also too easily interpreted as a guarantee of equivalence: same CAS = same material = same smell.

In practice, it is not that simple. A CAS number helps identify a registered chemical substance or defined material identity, but by itself it does not describe commercial grade, purity, isomer distribution, trace components, production process or the olfactory behaviour of a specific product.

For this reason, when buying perfumery raw materials, the CAS number is important — but it should be read together with the trade name, manufacturer, technical specifications and olfactory evaluation.

What is a CAS number?

CAS stands for Chemical Abstracts Service. A CAS Registry Number is a numerical identifier assigned to chemical substances registered in the CAS database.

Its main advantage is that it reduces naming ambiguity. The same substance may have several common names, synonyms or commercial designations; the CAS number provides a more stable technical reference for recognising it in documentation.

On a product page, the CAS number is therefore especially useful for:

• distinguishing substances with similar names;
• recognising synonyms;
• connecting technical data sheets, SDS documents and supplier documentation;
• checking that documents refer to the same general chemical identity.

What a CAS number does not tell you

A CAS number is not an olfactory description and it is not a quality mark. Two commercial products carrying the same CAS number can still differ in ways that matter both technically and olfactorily.

These differences may include:

• purity and the percentage of the main substance;
• isomer profile, where several isomers are possible;
• trace components and impurities resulting from the production process;
• stabilisers or antioxidants present in the commercial product;
• manufacturing process and manufacturer specifications;
• standardisation of the commercial grade.

In perfumery, differences that may look small analytically can still be perceptible to the nose, especially when a material has a very characteristic signature or is used at a significant level.

The same CAS does not automatically mean the same smell

This is the most important consequence for formulators and for anyone purchasing raw materials.

Two commercial grades may share the same CAS number yet differ in:

• intensity;
• transparency;
• texture;
• secondary facets;
• diffusion;
• tenacity;
• behaviour within a formula.

A 1:1 substitution based only on the CAS number can therefore be misleading. The CAS tells you that the products refer to the same general chemical identity, but it does not guarantee that they are olfactorily interchangeable.

An important example: HEDIONE® and HEDIONE® HC

The comparison between HEDIONE® and HEDIONE® HC clearly shows why a CAS number does not tell the whole story.

The two products occupy the same broad chemical and olfactory territory, but the HC grade has a different isomer distribution and a higher proportion of the more olfactorily active component. In a formula, this can translate into differences in floral presence, radiance and impact.

For the full comparison, see HEDIONE® vs HEDIONE® HC: differences and when to use them in perfumery.

Woody ambers also show the limits of relying on CAS alone

Within the woody-amber territory, commercial products that appear chemically close can still behave differently, even when their technical documentation suggests substantial overlap.

The comparison between ISO E SUPER®, TIMBERSILK™ and SYLVAMBER™ is a useful example of why trade name and actual commercial grade matter at least as much as the general chemical reference.

For a perfumer, the question is not only “which molecule is this?” but also:

• how transparent is it?
• how much volume does it create?
• how dry or soft is it?
• how does it integrate with other materials?
• how does it evolve in the drydown?

Chemical name, CAS number and trade name are not the same thing

A raw material can be identified on several levels at once.

For informed purchasing and formulation, these pieces of information should be read together. The trade name can be decisive when reproducing a formula with the same grade originally used.

CAS numbers are particularly useful for synonyms

In a perfumery raw-material catalogue, it is common to encounter substances known under several names. The CAS number helps identify when different names refer to the same underlying chemical identity.

This is especially useful when consulting documents from different manufacturers, technical literature or SDS documents, where nomenclature can vary.

For online purchasing, the CAS number is therefore an excellent search tool — as long as it is not treated as an absolute criterion of olfactory equivalence.

Does the same CAS mean the same safety profile or the same IFRA limits?

Not necessarily.

The CAS number identifies the substance, but regulatory documentation must be read for the actual commercial product being purchased. One grade may be an almost pure substance, another may contain declared stabilisers, diluents or other components, while a commercial base may be a mixture containing several CAS numbers.

This is why SDS documents, allergen declarations and IFRA documentation should not be replaced by a simple CAS search.

For more on the distinction between these documents, see SDS in perfumery: how to read a safety data sheet and IFRA Category 4: how to read and calculate limits correctly.

Commercial bases can contain multiple CAS numbers

A perfumery base is generally a formulated mixture created to provide an olfactory effect or function. It should therefore not be interpreted as a single molecule.

Its SDS may list several components relevant to hazard classification, but this does not mean that the complete formula of the base is public. A manufacturer can keep the composition proprietary while still providing the documentation required for professional use.

For more on this distinction, see Bases, accords and molecules in perfumery: what's the difference?.

How to read a CAS number on a product page

When you find a CAS number in the technical information for a raw material, use it mainly to answer three questions:

1. What is the general chemical identity of this material?
2. Which synonyms or alternative names might I encounter?
3. Does the documentation I am reading actually refer to the same substance?

To determine whether two products are genuinely equivalent for your work, you also need to consider commercial grade, manufacturer, specifications and olfactory behaviour.

Why we include CAS numbers in our raw-material technical data

In the La Profumiera di Venezia catalogue, CAS numbers are provided when available because they make product information more useful for the formulator: they facilitate searching, reduce ambiguity and help connect a product with its technical documentation.

But CAS numbers do not replace the other data. This is why trade name, manufacturer, material type, olfactory profile, function and available documents also matter in our technical information.

Conclusion

A CAS number is an important identification tool, but it is not an olfactory fingerprint.

The same CAS does not automatically mean the same smell, the same commercial quality or the same performance in a formula. A perfumer needs to read the chemical reference together with the actual product: manufacturer, specifications, grade, documentation and olfactory behaviour.

The CAS number mainly answers the question “what substance is this?”. To answer “how does this particular grade behave in perfumery?”, a broader level of information is required.