PEG-9 Methyl Ether Dimethicone: properties, uses, advantages, disadvantages, safety

PEG-9 Methyl Ether Dimethicone is a synthetic silicone polyether, meaning a silicone polymer derived from dimethicone to which a polyoxyethylene portion is chemically linked. It is used in cosmetics mainly as a surfactant-emulsifier, skin-conditioning agent and hair-conditioning agent.

The designation PEG-9 indicates that the polyoxyethylene portion contains an average of approximately 9 ethylene oxide (EO) units. It does not mean that the cosmetic contains nine free molecules of ethylene oxide: the EO-derived units are incorporated into the polymer structure.

The name PEG-9 METHYL ETHER DIMETHICONE is included in the European glossary of common cosmetic ingredient names, under entry 20206 of Commission Implementing Decision (EU) 2025/1175.

Description

PEG-9 Methyl Ether Dimethicone belongs to the family of silicone polyethers, materials in which a polysiloxane chain is combined with polyether groups.

The cosmetic nomenclature describes it as a system of dimethyl siloxanes and silicones modified with methyl-polyoxyethylene groups, trimethylsilyl-terminated and characterised by an average polyoxyethylene chain corresponding to approximately 9 moles of ethylene oxide.

The molecule therefore contains both:

• a silicone/lipophilic portion, compatible with silicones and oil phases;

• a more hydrophilic polyether portion, capable of interacting with water.

This amphiphilic structure explains its ability to position itself at the interface between normally poorly miscible phases and to function as a silicone emulsifier.

The Cosmetic Ingredient Review describes PEG-9 Methyl Ether Dimethicone as a siloxane polymer with an average n value of 9 and assigns it hair-conditioning, skin-conditioning and surfactant-emulsifying functions.

Production process

PEG-9 Methyl Ether Dimethicone is an entirely industrially manufactured ingredient. It is not a botanical extract and is not a naturally occurring silicone.

For the alkoxy polysiloxane family, the Cosmetic Ingredient Review describes hydrosilylation as a typical manufacturing process, in which a hydrogen dimethicone chain reacts with an unsaturated polyether compound, such as an allyl alkoxylate.

The polyether chain can be adjusted during manufacture to obtain the desired structure and degree of ethoxylation.

For PEG-9 Methyl Ether Dimethicone, the final result is a material in which the silicone and polyoxyethylene portions are chemically bonded, rather than simply physically mixed.

Industrial manufacture generally includes:

• synthesis of the polymer;

• controlled hydrosilylation reaction;

• control of the degree of ethoxylation;

• removal of volatile substances;

• purification;

• control of residual process substances;

• standardisation of physical properties.

The exact process can vary according to manufacturer and commercial grade.

Main substances contained

A high-purity PEG-9 Methyl Ether Dimethicone consists mainly of the silicone-polyether polymer itself.

It is not technically correct to describe it as a mixture containing separate:

dimethicone + PEG-9 + ethylene oxide.

These names instead describe structural portions of the final polymer.

Because it is a polymeric material characterised by a distribution of chain lengths, it does not necessarily have one single molecular weight that is identical for every molecule.

For the same reason, assigning one unique molecular formula and molecular weight is not appropriate in the same way as for a low-molecular-weight pure substance.

ECHA associates the generic CAS 68938-54-5 with the substance name “Siloxanes and Silicones, di-Me, 3-hydroxypropyl Me, ethers with polyethylene glycol mono-Me ether” and EC/List No. 614-827-5, without assigning one unique molecular formula.

Identification data and functions

The CAS number should be regarded as generic, because it identifies a family of related polymeric materials and may also be associated with other Methyl Ether Dimethicone materials having different average PEG chain lengths.

Indicative physicochemical properties

The exact characteristics depend on the commercial grade.

A well-documented example is Shin-Etsu KF-6016, consisting of 100% PEG-9 Methyl Ether Dimethicone. The following values are therefore indicative of this specific grade and should not be considered universal specifications for the INCI ingredient.

The relatively low HLB of this commercial grade reflects its strong affinity for the silicone phase and explains its use as a water-in-silicone emulsifier.

Shin-Etsu recommends it particularly for make-up and skincare formulations.

Cosmetics

PEG-9 Methyl Ether Dimethicone is mainly used when water, silicones and oily components must be combined in a stable cosmetic formulation.

As a silicone emulsifier, it can be particularly useful in:

• foundations;

• concealers;

• primers;

• skincare products;

• creams and lotions;

• emulsions containing high levels of silicones;

• hair-care products;

• formulations requiring good spreadability and uniform distribution.

The silicone portion promotes compatibility with dimethicone and other silicone fluids, while the polyether portion allows greater interaction with the aqueous phase.

The resulting formulations may provide:

• good slip;

• uniform spreading;

• smooth sensory properties;

• reduced greasy feel;

• improved distribution of pigments and oils.

The actual sensory effect depends on the complete formulation and not on this ingredient alone.

Skin conditioning

The skin-conditioning function means that the ingredient contributes to maintaining the skin in good cosmetic condition.

It should not be interpreted as a dermatological active ingredient.

PEG-9 Methyl Ether Dimethicone can mainly contribute to:

• improving spreadability;

• promoting more uniform product distribution;

• modifying skin feel;

• reducing the heavy feel of some oil phases;

• contributing to the formation of a cosmetically pleasant film.

It should not automatically be attributed therapeutic, repairing or healing effects on the skin.

Hair conditioning

As a hair-conditioning agent, PEG-9 Methyl Ether Dimethicone can contribute to the surface properties of the hair fibre.

The silicone component may improve:

• slip;

• combability;

• softness;

• tactile feel;

• uniform distribution of the formulation over the hair.

The actual effect depends on concentration, the overall formulation and the presence of other silicones, surfactants and conditioning agents.

Advantages

PEG-9 Methyl Ether Dimethicone combines the typical compatibility of silicones with a more hydrophilic polyether component within the same molecular structure.

This characteristic makes it particularly useful for stabilising systems in which water and silicones must coexist.

It can:

• improve product spreadability;

• improve distribution;

• contribute to sensory properties;

• act simultaneously as an emulsifier and conditioning agent;

• improve compatibility between aqueous and silicone phases;

• support stable water-in-silicone emulsions.

Certain commercial grades also make it possible to prepare water-in-silicone emulsions at room temperature, which can simplify formulation and manufacturing processes.

The ingredient is chemically well characterised as a polymer family, and the Cosmetic Ingredient Review evaluated PEG-9 Methyl Ether Dimethicone within the alkoxy polysiloxane group as safe as used under the cosmetic-use conditions considered.

Disadvantages

PEG-9 Methyl Ether Dimethicone is a synthetic ingredient and is therefore not suitable for formulations whose commercial or formulation objective is to use only natural or minimally processed raw materials.

Because it is a polymer, the INCI name alone does not reveal precisely:

• molecular-weight distribution;

• viscosity;

• HLB;

• active-content percentage;

• impurity profile;

• exact emulsion behaviour.

These characteristics must be verified from the technical data sheet and certificate of analysis of the specific commercial grade used.

In addition, as with other ethoxylated ingredients, manufacturing quality is important to minimise potential contaminants associated with the ethoxylation process.

PEG, ethylene oxide and 1,4-dioxane

The presence of the abbreviation PEG is sometimes incorrectly interpreted as meaning that free ethylene oxide is present in the cosmetic.

This is not the case.

Ethylene-oxide-derived units are incorporated into the polyether chain of the polymer.

The relevant industrial quality issue is instead the possible formation of trace amounts of 1,4-dioxane during manufacture of certain ethoxylated ingredients.

The US FDA explains that 1,4-dioxane is not normally intentionally added to cosmetics but may occur as a manufacturing by-product in ingredients identified by terms such as:

• PEG;

• polyethylene glycol;

• polyoxyethylene;

• ingredient names containing “-eth-”.

The FDA has long recommended manufacturing techniques such as vacuum stripping to minimise these residues.

European scientific assessments have also considered very low residual concentrations of 1,4-dioxane in finished cosmetic products when evaluating consumer safety.

This means that the relevant issue is a process impurity requiring control, not PEG-9 Methyl Ether Dimethicone itself.

For professional assessment of a raw material, supplier documentation should therefore be checked for:

• 1,4-dioxane;

• residual ethylene oxide;

• purity;

• volatile substances;

• other relevant manufacturing impurities.

Safety

The Cosmetic Ingredient Review (CIR) assessed PEG-9 Methyl Ether Dimethicone within the family of alkoxy polysiloxanes.

Earlier evaluations of dimethicone copolyols generally indicated:

• low toxicity;

• limited penetration across biological membranes;

• low irritation potential under the conditions studied.

The CIR assessment included PEG-9 Methyl Ether Dimethicone among ingredients considered safe as used in cosmetic practices and concentrations covered by the assessment.

This conclusion must be interpreted correctly.

It does not mean that any concentration, exposure route or formulation is automatically safe.

Safety depends on:

• concentration in the finished product;

• area of application;

• leave-on or rinse-off use;

• possible eye exposure;

• possible aerosol exposure;

• impurity profile of the raw material;

• characteristics of the complete formulation.

European Union cosmetic regulation

The name PEG-9 METHYL ETHER DIMETHICONE appears in the official European glossary of common cosmetic ingredient names established by Commission Implementing Decision (EU) 2025/1175, under entry 20206.

Its inclusion in the glossary primarily establishes the common ingredient name used for cosmetic labelling.

It should not be interpreted, by itself, as unrestricted approval for use at any concentration.

Under Regulation (EC) No 1223/2009, the fundamental requirement remains that the finished cosmetic product must be safe under normal or reasonably foreseeable conditions of use and must undergo a cosmetic-product safety assessment before being placed on the market.

The safety assessment must also consider, where relevant:

• impurities;

• traces;

• raw-material quality;

• exposure conditions;

• toxicological profile.

United States

In the United States, cosmetic ingredients are generally subject to the requirement that finished cosmetics must be safe for consumers under labelled or customary conditions of use.

The Cosmetic Ingredient Review, although independent from the FDA, has specifically reviewed PEG-9 Methyl Ether Dimethicone as part of the alkoxy polysiloxane group and concluded that it is safe as used under the practices and concentrations considered.

The FDA additionally identifies 1,4-dioxane as a potential manufacturing contaminant of some ethoxylated cosmetic ingredients and recommends manufacturing controls to minimise its presence.

Environment

Specific environmental data for PEG-9 Methyl Ether Dimethicone are less extensive than for some simpler silicone materials.

It is not technically correct to transfer automatically to this ingredient all conclusions relating to:

• dimethicone;

• cyclic siloxanes;

• unmodified PEGs.

Its structure contains both:

• a polysiloxane fraction;

• a polyether fraction.

Environmental behaviour, degradation and partitioning may therefore differ from those of the individual starting-material families.

For a professional environmental assessment, the most appropriate sources are:

• the SDS of the specific commercial grade;

• available REACH information;

• manufacturer-specific environmental data;

• biodegradation and partitioning studies where available.

It should not automatically be described either as a biodegradable silicone or as a persistent silicone without ingredient-specific evidence.

Conclusion

PEG-9 Methyl Ether Dimethicone is a synthetic silicone polyether, produced by chemically modifying a dimethicone-type polysiloxane structure with a polyoxyethylene chain containing an average of approximately 9 EO units.

It is not a physical mixture of free PEG and dimethicone, but a chemically modified polymer containing both a silicone-compatible region and a more hydrophilic polyether region.

This structure explains its principal cosmetic functions as:

• surfactant-emulsifier;

• skin-conditioning agent;

• hair-conditioning agent.

The generic CAS 68938-54-5 is associated with this polymer family, while ECHA lists EC/List No. 614-827-5. Because the material is polymeric, it does not have one universal molecular formula or molecular weight applicable to every chain in the material.

From a formulation standpoint, PEG-9 Methyl Ether Dimethicone is particularly useful in silicone-containing emulsions. A documented commercial example, Shin-Etsu KF-6016, has a calculated HLB of approximately 4.5 and is marketed as a water-in-silicone emulsifier, although these numerical properties should be regarded as specific to that commercial grade rather than universal for every material carrying the same INCI name.

The Cosmetic Ingredient Review assessed PEG-9 Methyl Ether Dimethicone as safe as used under the cosmetic-use conditions considered.

The main quality consideration associated with the PEG portion concerns proper control of manufacturing impurities, particularly possible trace 1,4-dioxane generated during ethoxylation. This impurity can be substantially reduced through appropriate purification methods and should be assessed through supplier specifications and certificates of analysis.

Overall, PEG-9 Methyl Ether Dimethicone can be regarded as a well-characterised functional cosmetic ingredient, particularly useful as a silicone emulsifier and conditioning agent, provided that it is used in a properly safety-assessed formulation and supplied as an appropriately purified and documented cosmetic-grade raw material.