Ingredient review
Polymethylstyrene Isopropanol Ketone
INCI: POLY METHYL STYRENE ISOPROPANOL KETONE
A synthetic film former that helps makeup last longer and resist water, but it's not a skincare active and may feel heavy on some skin types.
In plain English
This is a man-made ingredient that creates a thin, flexible film on your skin or hair. It's used in products like long-wear foundation and waterproof mascara to help them stay put and resist sweat or water. Think of it like a clear, invisible shield that holds the product in place. It doesn't moisturize or treat your skin—it's purely a texture and performance booster.
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
Polymethylstyrene Isopropanol Ketone 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 Polymethylstyrene Isopropanol Ketone.
- 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 polymer derived from styrene and isopropanol ketone, engineered to form a flexible, water-resistant film on the skin or hair. It is not a natural or biodegradable ingredient.
How it works
When applied, the polymer chains spread across the skin and link together as the solvent evaporates, creating a continuous film. This film locks in pigments and other ingredients, reducing transfer and improving wear time. It also helps control viscosity, giving products a smooth, spreadable texture.
Pros
Boosts makeup longevity
Creates a durable film that helps foundation, mascara, and lip products stay in place for hours, even in humid conditions.
Water and sweat resistant
Forms a barrier that repels moisture, making it ideal for active lifestyles or special occasions.
Cons and cautions
No skincare benefit
This ingredient is purely functional—it doesn't hydrate, soothe, or improve skin health, so it's best paired with a good skincare routine underneath.
Can feel heavy or tight
On dry or sensitive skin, the film may create a noticeable tightness or a 'mask-like' feel, especially in high concentrations.
Best for
- Anyone wanting long-lasting, waterproof makeup
- People with oily skin who struggle with makeup fading
Use caution if
- Those with very dry or dehydrated skin who prefer lightweight, breathable formulas
Usage tips
Safety summary
Considered safe for topical use in cosmetics at typical concentrations. Low irritation and comedogenic potential, but may cause tightness on very dry skin. Not intended for ingestion or eye contact.
Research notes
Limited peer-reviewed studies specifically on this polymer, but it is structurally similar to other film-forming polymers that have been evaluated for safety by the Cosmetic Ingredient Review (CIR) panel. No significant toxicity concerns have been reported.
Common label clues
- Typical concentration
- Typically 1–10% in leave-on formulas
- Regulatory status
- Approved for use in cosmetics in the EU, US, and many other regions. No specific restrictions, but always follow local regulations.
- Common uses
- Long-wear foundations, Waterproof mascaras, Lip products, Sunscreens
- Environmental note
- As a synthetic polymer, it is not biodegradable and may contribute to microplastic pollution if washed into waterways. Some brands are moving toward bio-based alternatives.
Good to know
- This ingredient is often listed near the end of an INCI because it's used in low to moderate concentrations.
- It is not biodegradable and is derived from non-renewable petrochemicals, which may be a concern for eco-conscious consumers.
Common questions
What is Polymethylstyrene Isopropanol Ketone in beauty products?
This is a man-made ingredient that creates a thin, flexible film on your skin or hair. It's used in products like long-wear foundation and waterproof mascara to help them stay put and resist sweat or water. Think of it like a clear, invisible shield that holds the product in place. It doesn't moisturize or treat your skin—it's purely a texture and performance booster.
What does Polymethylstyrene Isopropanol Ketone do in a beauty product?
When applied, the polymer chains spread across the skin and link together as the solvent evaporates, creating a continuous film. This film locks in pigments and other ingredients, reducing transfer and improving wear time. It also helps control viscosity, giving products a smooth, spreadable texture.
Is Polymethylstyrene Isopropanol Ketone safe for most people?
Considered safe for topical use in cosmetics at typical concentrations. Low irritation and comedogenic potential, but may cause tightness on very dry skin. Not intended for ingestion or eye contact.
Who should be careful with Polymethylstyrene Isopropanol Ketone?
Those with very dry or dehydrated skin who prefer lightweight, breathable formulas
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.