Ingredient review
Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer
INCI: ISOSTEAROYL TRIMELLITIC ANHYDRIDE/TRIMETHYLOLPROPANE COPOLYMER
A synthetic polymer that helps makeup and sunscreen stay put, but may feel heavy or tight on some skin types.
In plain English
This is a man-made ingredient that forms a thin, flexible film on your skin or hair. Think of it like a clear, breathable plastic wrap that helps other ingredients stay in place, resist water, and last longer. It's commonly found in long-wear makeup, waterproof sunscreens, and styling products.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer is generally a lower-concern ingredient when the full formula suits your skin.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
A synthetic copolymer created by reacting isostearic acid derivatives with trimellitic anhydride and trimethylolpropane. It belongs to a class of film-forming polymers designed to improve product wear and water resistance.
How it works
When applied, the polymer dries into a continuous, flexible film that adheres to the skin or hair surface. This film physically locks in pigments, UV filters, or styling agents, reducing transfer, smudging, and wash-off from water or sweat.
Pros
Boosts wear time
Helps makeup and sunscreen resist smudging, fading, and water exposure for hours.
Creates a smooth finish
The film evens out the skin's surface, making foundation or concealer look more polished.
Cons and cautions
Can feel tight
On dry or sensitive skin, the film may create a pulling or uncomfortable sensation.
Requires double cleansing
Water alone won't remove it; you'll likely need an oil-based cleanser or micellar water.
Best for
- People who want long-wearing makeup or waterproof sunscreen
- Those with oily or combination skin who prefer a matte finish
Use caution if
- Individuals with very dry or dehydrated skin who dislike a tight feeling
Usage tips
Safety summary
Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer is considered safe for cosmetic use at typical concentrations. It has low irritation and comedogenic potential, though individuals with very sensitive or dry skin may find it uncomfortable.
Research notes
Safety assessments rely on general polymer toxicology and industry experience. No specific peer-reviewed studies on this exact copolymer were found, but similar film-forming polymers have a long history of safe use in cosmetics.
Common label clues
- Typical concentration
- 1% to 10%
- Regulatory status
- Approved for use in cosmetics in the US, EU, and other major markets. No specific concentration restrictions are common, but formulators follow good manufacturing practices.
- Common uses
- Long-wear foundations, Waterproof mascaras, Sunscreens, Hair styling products
- Environmental note
- As a synthetic polymer, it is not readily biodegradable. However, it is used in small amounts and is not known to accumulate significantly in the environment.
Good to know
- This polymer is often combined with other film formers to fine-tune flexibility and feel.
- It is considered safe for use in cosmetics by major regulatory bodies at typical concentrations.
Common questions
What is Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer in beauty products?
This is a man-made ingredient that forms a thin, flexible film on your skin or hair. Think of it like a clear, breathable plastic wrap that helps other ingredients stay in place, resist water, and last longer. It's commonly found in long-wear makeup, waterproof sunscreens, and styling products.
What does Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer do in a beauty product?
When applied, the polymer dries into a continuous, flexible film that adheres to the skin or hair surface. This film physically locks in pigments, UV filters, or styling agents, reducing transfer, smudging, and wash-off from water or sweat.
Is Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer safe for most people?
Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer is considered safe for cosmetic use at typical concentrations. It has low irritation and comedogenic potential, though individuals with very sensitive or dry skin may find it uncomfortable.
Who should be careful with Isostearoyl Trimellitic Anhydride/Trimethylolpropane Copolymer?
Individuals with very dry or dehydrated skin who dislike a tight feeling
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.