What Is Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer?
Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer is a man-made ingredient created by combining glycol with two types of aromatic esters: sodium dimethyl sulfoisophthalate and dimethyl terephthalate. When these building blocks are reacted together they form a long, chain-like molecule called a copolymer. This structure gives the material a lightweight but sturdy character that can bulk up a formula without feeling heavy on the skin.
The copolymer traces its cosmetic use back to the late twentieth century when chemists were searching for alternatives to natural fillers that could keep creams and lotions stable under different temperatures. By tweaking the ratios of its three starting materials they found a polymer that dispersed evenly in water-based products and stayed smooth over time. That reliability earned it a spot in many everyday items such as facial moisturizers, rinse-off masks, sunscreens, serums and liquid foundations.
Manufacturing begins with the separate production of glycol and the two ester monomers. These raw materials are fed into a large reactor where heat and a catalyst drive the polymerization step. Once the copolymer chains reach the desired length the mixture is cooled, purified and ground into a fine powder or turned into an aqueous dispersion. Cosmetic brands then add this ready-to-use form to their batches during the mixing stage.
Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer’s Cosmetic Benefits/Uses
In skincare and makeup formulas this ingredient serves one key purpose that boosts product performance.
Its main role is bulking. Acting as a volume builder it increases the overall mass of a cream, lotion or gel without changing its active levels. This helps brands achieve a pleasing texture, makes the product easier to spread and can reduce the need for heavier waxes or oils. The result is a lighter feel on the skin while still giving users the amount of product they expect from each pump or scoop.
Who Can Use Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer
This copolymer is considered suitable for every skin type including oily, dry, combination and sensitive skin because it is chemically inert and does not interact with skin lipids or pH. People with very reactive or allergy-prone skin can typically tolerate it although, as with any ingredient, individual sensitivities are possible.
The material is synthetic and made without animal-derived substances which makes it appropriate for vegans and vegetarians.
No data indicate that the ingredient is absorbed in amounts that would pose a risk to pregnant or breastfeeding women. That said this is not medical advice and anyone who is expecting or nursing should consult a healthcare professional before introducing new products just to be safe.
The copolymer does not cause photosensitivity so it will not make skin more prone to sunburn when used during the day.
Potential Side Effects/Adverse Reactions
Responses to topical Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer vary from person to person. The points below outline potential side effects although they are uncommon for most users when the ingredient is formulated correctly.
- Mild stinging or redness in very sensitive skin
- Rare cases of contact dermatitis for individuals allergic to similar aromatic esters
- Transient eye irritation if the product accidentally gets into the eyes
- Potential for product build-up that feels filmy on skin if used in high-load formulas
If any irritation or discomfort occurs discontinue use and seek advice from a medical professional.
Comedogenic Rating
Rating: 0 / 5
This polymer is a large, water-dispersible molecule that sits on the surface rather than sinking into pores. It contains no oily or waxy fractions that could harden inside follicles so it is classed as non-comedogenic.
Suitable for acne-prone and breakout-prone skin.
Because it does not create an occlusive film, it is unlikely to trap sebum or debris that might otherwise lead to clogged pores.
Summary
Ethylene/Sodium Sulfoisophthalate/Terephthalate Copolymer is used mainly as a bulking agent that builds volume in creams, lotions and gels while keeping the texture light. Its long, stable chains disperse uniformly through water-based formulas which helps products keep a smooth feel and consistent viscosity over time.
Although not a headline ingredient, it is a quiet workhorse that shows up in a fair number of mainstream moisturizers, sunscreens and liquid foundations because it is reliable, cost-effective and vegan-friendly.
Current research and industry evaluations rate it as low risk for irritation or pore blockage so it is considered safe for regular use. As with any new skincare item, a small patch test is wise to confirm personal compatibility.