What does PEG-100 stearate do in a cream?

It emulsifies — it keeps the oil and water phases mixed so the product stays a cream instead of splitting into layers. It has no effect on skin of its own.

Why is it always next to glyceryl stearate?

The two are sold and used as a pair because their emulsifier balance is complementary: glyceryl stearate is the oil-loving half, PEG-100 stearate the water-loving one. Together they make a stable, pleasant-feeling lotion that neither manages alone.

Is the 1,4-dioxane concern real?

The by-product is real; the exposure is the part usually left out. It forms during ethoxylation and is stripped out before the ingredient is sold, and cosmetic-grade material is specified to trace levels. It is a manufacturing control question, not an inherent property of the ingredient.

Is it safe on broken or compromised skin?

PEGs raise penetration through damaged skin, and safety reviews have advised against applying them to badly compromised or burned skin. On intact skin, including sensitive skin, this does not apply.

Is PEG-100 stearate comedogenic?

There is no reliable rating for it. Comedogenicity depends far more on the finished formula than on a single emulsifier, so treat any number attached to it with suspicion.

PEG-100 Stearate — Ingredient Guide

How it works

PEG-100 stearate is stearic acid that has been ethoxylated — roughly a hundred ethylene oxide units strung on as a water-loving tail, leaving the fatty stearate end oil-loving. That split personality is the whole job: sitting at the boundary between the oil and water phases, it lowers the surface tension between them so that oil droplets stay dispersed instead of separating out. On its own it is too water-loving to build a stable cream, which is why the label almost always reads Glyceryl Stearate (and) PEG-100 Stearate. The pair covers both sides of the emulsifier balance and gives lotions the body and slip most people expect from them.

The evidence

There is nothing to prove about efficacy, because it makes no claim on skin. The relevant literature is safety: the Cosmetic Ingredient Review panel has assessed PEG stearates as safe in the present practices of use and concentration, with minimal skin and eye irritation in testing. One qualification is worth keeping: PEGs increase penetration through damaged skin, which is why the CIR review has consistently advised against using them on badly compromised or burned skin. On intact skin that caveat does not apply.

Suitability

Suitable for all skin types, in the sense that it is not aimed at any of them. Contact allergy to PEG emulsifiers is documented but genuinely uncommon; where it occurs it is usually found on patch testing rather than guessed at. If a moisturiser stings, the emulsifier is a much less likely culprit than the fragrance, preservative or active in the same jar.

Concentration

Typically 1% to 5%, chosen by the formulator to match the oil load rather than by any regulatory ceiling — neither the EU nor the US imposes one. Its concentration is not something a shopper can usefully act on: too little and the cream separates, too much and it feels soapy, and both are the formulator's problem rather than the reader's.

Conflicts & combinations

No meaningful conflicts with actives. The 1,4-dioxane question is the one worth answering plainly: it is a carcinogenic by-product that can form during ethoxylation, it is not deliberately added, and it is removed by vacuum stripping before the raw material ships, with cosmetic-grade suppliers holding it to trace limits. That makes it a supply-chain quality issue with a well-established control, not a reason to read PEG on an ingredient list as a warning.