What Is Peg-3 Trimethylolpropane Triisostearate?
Peg-3 Trimethylolpropane Triisostearate is a multi-functional liquid ester created by linking trimethylolpropane, a small alcohol, with three molecules of isostearic acid that have been lightly ethoxylated. That ethoxylation step gives the ingredient its “PEG-3” prefix and adds just enough water-loving character to balance the naturally oily isostearic acid. The finished material is a clear to slightly hazy fluid that feels silky rather than greasy.
Although the individual building blocks—trimethylolpropane, ethylene oxide and isostearic acid—have been used in industrial chemistry since the mid-20th century, cosmetic chemists began combining them in the 1990s while looking for modern skin conditioners that could replace heavier plant oils and petrolatum. The resulting ester proved to be stable, easy to spread and highly compatible with both water-based and oil-based formulas, which quickly made it popular in makeup and skincare.
Manufacturing starts with purified trimethylolpropane, which is first reacted with a controlled amount of ethylene oxide to add three “PEG” units. The partially ethoxylated alcohol is then esterified with high-purity isostearic acid derived from vegetable oils like rapeseed or soybean. The process is done under vacuum to remove water, producing a low-odor fluid that meets cosmetic grade standards.
You will most often see Peg-3 Trimethylolpropane Triisostearate in color cosmetics such as liquid foundations, lipsticks and cream blushes because it helps pigments spread evenly and improves wear time. It also shows up in moisturizers, cleansing balms, makeup removers, sunscreens and anti-aging serums where a lightweight emollient with good skin feel is needed.
Peg-3 Trimethylolpropane Triisostearate’s Cosmetic Benefits/Uses
Formulators reach for this ingredient primarily for one reason
Skin conditioning: It forms a soft, flexible film that smooths the skin surface, delivering immediate softness and a subtle sheen. By blending the slip of silicones with the nourishment of plant oils, it leaves skin feeling hydrated without a heavy or sticky afterfeel. This conditioning effect also improves the texture of makeup, helping products glide on evenly and stay comfortable throughout the day.
Who Can Use Peg-3 Trimethylolpropane Triisostearate
This silky ester suits most skin types. Its light non sticky texture makes it comfortable for normal, dry and combination skin while the low oiliness keeps it from overwhelming oily or acne prone skin. Very sensitive skin may prefer a short test period because the PEG portion could cause slight irritation in rare cases.
The material is made from plant based isostearic acid and synthetic alcohol, with no animal sourced inputs, so it is appropriate for both vegans and vegetarians.
No data point to risks for women who are pregnant or breastfeeding when the ingredient is used in cosmetics. Absorption through intact skin is minimal, yet this is not medical advice and anyone expecting or nursing should review every product with their doctor before use.
Peg-3 Trimethylolpropane Triisostearate does not increase photosensitivity, and it is odorless so it will not react with sunlight to create smell or color changes on skin. It is also free of common allergens like gluten, soy and nuts, which broadens its compatibility profile.
Potential Side Effects/Adverse Reactions
Responses to topical Peg-3 Trimethylolpropane Triisostearate differ from person to person. The issues listed below are only potential outcomes and are not expected for the average user when the ingredient is formulated correctly.
- Mild redness or stinging on very sensitive skin
- Contact dermatitis in individuals allergic to PEG based compounds
- Temporary eye irritation if the product unintentionally enters the eyes
- Rare clogging of pores in those extremely prone to acne
If any of these effects develop discontinue use and seek guidance from a healthcare professional.
Comedogenic Rating
Rating: 1/5
Peg-3 Trimethylolpropane Triisostearate is a lightweight ester with partial water solubility from its small PEG portion. That balance lets it spread thinly and rinse off more easily than heavier oils so it is unlikely to sit in pores and oxidize. The isostearic acid backbone is branched, which further reduces its tendency to stack and block follicles. Lab tests and user reports show little evidence of persistent clogging, earning it a low score of 1.
Because of this mild profile the ingredient is generally considered acceptable for people who are prone to acne or occasional breakouts.
As with any emollient, very heavy use in thick balms or layering multiple products could tip the scale for some ultra sensitive skins, but in most mainstream formulas the risk remains low.
Summary
Peg-3 Trimethylolpropane Triisostearate is valued for its skin conditioning power. It forms a smooth breathable film that softens skin, boosts slip and helps pigments glide evenly so makeup looks fresh longer. The tiny PEG segment adds a hint of water affinity which keeps the ester from feeling greasy while the branched isostearate tail delivers lasting comfort.
The ingredient enjoys steady use in liquid foundations, lipsticks, cleansing balms and modern moisturizers though it is not as famous as silicones or classic plant oils. Formulators appreciate its versatility and clean sensory profile.
Safety data show low irritation and minimal comedogenicity for most users. Still, everyone’s skin is unique so it is wise to patch test any new product that features this ester to confirm personal compatibility.