Ingredient review
Polyethylene Isoterphthalate
INCI: POLYETHYLENE ISOTEREPHTHALATE
A synthetic polymer that helps products form a flexible film on skin or lashes, but offers no active skincare benefits.
In plain English
Polyethylene Isoterphthalate is a plastic-like ingredient used in cosmetics to create a thin, flexible film on the skin or lashes. It helps mascara stay on your lashes without flaking and gives lip products a smooth, long-lasting feel. Think of it as a clear, invisible coating that helps makeup stay put. It doesn't moisturize or treat the skin—it's purely a performance ingredient for texture and wear.
Review score
Safety, usefulness, and evidence
Useful in the right context, but not low-maintenance
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
Read the cautions before using
Polyethylene Isoterphthalate 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 Polyethylene Isoterphthalate.
- 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 polyester polymer derived from petroleum, engineered to form a continuous, flexible film when applied to surfaces like skin, lashes, or nails.
How it works
When the product dries, the polymer molecules link together into a thin, clear film that adheres to the surface. This film resists water and oil, helping makeup last longer and reducing smudging or transfer.
Pros
Long-wearing performance
Helps mascara and eyeliners resist smudging, flaking, and running throughout the day.
Flexible film
The film it forms is flexible, so it moves with your skin or lashes without cracking or feeling stiff.
Cons and cautions
No skincare benefit
It does not hydrate, soothe, or protect the skin—it's purely a cosmetic film-former.
Synthetic origin
Derived from petroleum, which may be a concern for those seeking sustainable or natural ingredients.
Best for
- Anyone wanting long-wearing mascara or eyeliner
- People who prefer smudge-proof lip products
Use caution if
- Those seeking purely natural or plant-based cosmetics
- Individuals with very sensitive eyes who react to film-forming polymers
Usage tips
Safety summary
Generally recognized as safe for topical cosmetic use at typical concentrations. Low irritation and comedogenic risk, but no active benefits for skin health.
Research notes
Limited peer-reviewed studies specific to this polymer in cosmetics. Safety is inferred from its chemical class (polyesters) and long history of use in personal care products.
Common label clues
- Typical concentration
- Typically 1–10% in leave-on products
- Regulatory status
- Approved for use in cosmetics in the US (FDA) and EU (CosIng) with no specific concentration restrictions.
- Common uses
- Mascara, Eyeliners, Lip products, Nail polish
- Environmental note
- As a synthetic polymer, it is not biodegradable and may contribute to microplastic pollution if rinsed down drains.
Good to know
- Often listed near the end of ingredient lists because it's used in small amounts.
- Commonly found in 'waterproof' or 'long-wear' makeup formulas.
Common questions
What is Polyethylene Isoterphthalate in beauty products?
Polyethylene Isoterphthalate is a plastic-like ingredient used in cosmetics to create a thin, flexible film on the skin or lashes. It helps mascara stay on your lashes without flaking and gives lip products a smooth, long-lasting feel. Think of it as a clear, invisible coating that helps makeup stay put. It doesn't moisturize or treat the skin—it's purely a performance ingredient for texture and wear.
What does Polyethylene Isoterphthalate do in a beauty product?
When the product dries, the polymer molecules link together into a thin, clear film that adheres to the surface. This film resists water and oil, helping makeup last longer and reducing smudging or transfer.
Is Polyethylene Isoterphthalate safe for most people?
Generally recognized as safe for topical cosmetic use at typical concentrations. Low irritation and comedogenic risk, but no active benefits for skin health.
Who should be careful with Polyethylene Isoterphthalate?
Those seeking purely natural or plant-based cosmetics Individuals with very sensitive eyes who react to film-forming polymers
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.