Ingredient review
Bis-Arachidyl PEG-400/SMDI Copolymer
INCI: BIS-ARACHIDYL PEG-400/SMDI COPOLYMER
A synthetic film-former that helps products stay put longer, but it may feel heavy or tight on some skin types.
In plain English
This is a man-made polymer that forms a thin, flexible film on your skin or hair. Think of it like a clear, breathable wrap that helps makeup or sunscreen stay in place longer, even when you sweat or get wet. It's often used in waterproof and long-wear 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
Bis-Arachidyl PEG-400/SMDI 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 Bis-Arachidyl PEG-400/SMDI 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 arachidyl alcohol (a fatty alcohol from plants) with PEG-400 (a polyethylene glycol chain) and SMDI (saturated methylene diphenyl diisocyanate). The result is a large molecule that can spread into a uniform, water-resistant film.
How it works
When applied, the copolymer's molecules link together as the solvent (water or alcohol) evaporates, forming a continuous, flexible film. This film physically blocks water and oil from reaching the underlying product, improving wear time and water resistance without feeling overly stiff.
Pros
Strong water resistance
Creates a durable barrier that helps sunscreen and makeup survive sweat, humidity, and swimming without breaking down.
Flexible film
Unlike some older film-formers, this copolymer stays flexible, so it won't crack or flake as you move your face or hair.
Cons and cautions
Can feel heavy
On dry or sensitive skin, the film may feel tight, sticky, or like a second layer, especially in high concentrations.
Removal difficulty
Because it's water-resistant, a standard gentle cleanser may not fully remove it, often requiring an oil-based or double-cleansing step.
Best for
- People who want long-wearing, water-resistant makeup or sunscreen
- Those with normal to oily skin who don't mind a slight film feel
Use caution if
- Individuals with very dry or sensitive skin who may find the film uncomfortable
- Anyone who prefers minimal, easily removable products
Usage tips
Safety summary
Generally considered safe for topical use at typical concentrations. The PEG component is well-tolerated, and the polymer is too large to penetrate the skin significantly. However, individuals with very sensitive skin may experience mild irritation or tightness.
Research notes
Limited independent studies on this specific copolymer, but its class (polyurethane-based film-formers) has been evaluated by the Cosmetic Ingredient Review (CIR) panel and found safe for use in cosmetics when formulated properly.
Common label clues
- Typical concentration
- 0.5% to 5%
- Regulatory status
- Approved for use in cosmetics in the US, EU, and many other regions. The EU CosIng database lists it as a film-forming agent with no specific restrictions at typical use levels.
- Common uses
- Water-resistant sunscreens, Long-wear foundations, Waterproof mascaras, Hair styling products
- Environmental note
- As a synthetic polymer, it is not biodegradable and may contribute to microplastic pollution. Some manufacturers are exploring bio-based alternatives.
Good to know
- This ingredient is often found in 'waterproof' and 'long-wear' formulas, but it is not a sunscreen active ingredient itself.
- The 'PEG-400' part indicates a polyethylene glycol chain of about 400 units, which helps the polymer spread evenly.
Common questions
What is Bis-Arachidyl PEG-400/SMDI Copolymer in beauty products?
This is a man-made polymer that forms a thin, flexible film on your skin or hair. Think of it like a clear, breathable wrap that helps makeup or sunscreen stay in place longer, even when you sweat or get wet. It's often used in waterproof and long-wear products.
What does Bis-Arachidyl PEG-400/SMDI Copolymer do in a beauty product?
When applied, the copolymer's molecules link together as the solvent (water or alcohol) evaporates, forming a continuous, flexible film. This film physically blocks water and oil from reaching the underlying product, improving wear time and water resistance without feeling overly stiff.
Is Bis-Arachidyl PEG-400/SMDI Copolymer safe for most people?
Generally considered safe for topical use at typical concentrations. The PEG component is well-tolerated, and the polymer is too large to penetrate the skin significantly. However, individuals with very sensitive skin may experience mild irritation or tightness.
Who should be careful with Bis-Arachidyl PEG-400/SMDI Copolymer?
Individuals with very dry or sensitive skin who may find the film uncomfortable Anyone who prefers minimal, easily removable products
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.