Phenoxyethanol Blends and the CAS Behind Each Part

Phenoxyethanol rarely shows up alone in a supplier catalog. It's almost always sold pre-mixed with something else, most commonly a paraben or ethylhexylglycerin, because those combinations broaden the spectrum of microbial protection compared to phenoxyethanol on its own. That's convenient for formulating, and slightly annoying for filing, because it means your CNF line item is never just "Phenoxyethanol."

Why phenoxyethanol gets paired up

Phenoxyethanol alone handles a fairly broad range of bacteria and some fungi but benefits from a partner ingredient to round out its coverage, especially against certain molds and yeasts. Ethylhexylglycerin is a common pairing partner that also functions as a skin-feel enhancer and can boost the preservative efficacy of phenoxyethanol through a synergistic effect. Paraben pairings, using one or more paraben esters, are the other long-standing combination, though paraben-free formulating has pushed a lot of brands toward the ethylhexylglycerin route instead.

Two common systems, broken into parts

Phenoxyethanol and ethylhexylglycerin system

INCI name	Typical function	Note
Phenoxyethanol	Preservative	Has an established CAS number; verify with your supplier's documentation since some substances carry more than one registered CAS
Ethylhexylglycerin	Preservative booster, skin conditioning	Also has its own established CAS number

Phenoxyethanol and paraben system

INCI name	Typical function	Note
Phenoxyethanol	Preservative	Same as above
Methylparaben, Ethylparaben, Propylparaben, or Butylparaben (varies by supplier formulation)	Preservative	Each paraben ester is its own distinct INCI name and CAS number, not interchangeable on paper even when the functional role is similar

The paraben row is the one people most often get wrong, because "parabens" gets used casually as a category name in marketing copy, but on a filing each specific paraben ester used needs its own line with its own CAS number. A blend labeled by a supplier as "Phenoxyethanol and Paraben Blend" might specifically be methylparaben and propylparaben, or a different combination entirely. You need the supplier's actual composition to know which.

Getting the real percentages

Same math as any other blend. If your formula uses 0.8% of a preservative system that is 90% phenoxyethanol and 10% ethylhexylglycerin, your finished product contains 0.72% phenoxyethanol and 0.08% ethylhexylglycerin. Those are the two numbers that go on the CNF and, in appropriate form, on the label, not "0.8% Preservative System."

Where CAS confusion tends to creep in

Some substances legitimately have more than one CAS number registered historically, which can make cross-referencing supplier documents against regulatory databases feel inconsistent even when everyone is naming the same substance correctly. If a supplier's SDS lists a CAS number that looks different from what you expected, don't assume it's an error before checking. It may be an alternate registered number for the same INCI-named substance. When something looks off, cross-check the INCI name itself first, since that's the anchor the Hotlist screening actually keys on.

Practical checklist before you file

• Request the exact composition ratio of any preservative blend from your supplier, not just the trade name and a vague "contains phenoxyethanol" statement.
• Confirm which specific paraben esters are present if the blend includes any, since "parabens" is not itself an INCI name.
• Do the multiplication to get real finished-product percentages for each component.
• Check each component's Hotlist status individually. A perfectly ordinary preservative combination can still have a concentration cap worth double-checking against your actual use level.
• Keep the supplier composition documentation on file. If you ever amend the formula or a supplier changes their ratio, you'll want that paper trail rather than reconstructing it from memory.

Cosmetic Comply expands supplier blends like these automatically, mapping each component to its INCI name and CAS number and carrying the real percentage through to the Hotlist screen, so a preservative system doesn't sit on your filing as an unresolved black box.