Ingredient review

PEG-400/1,4-Butanediol/SMDI Copolymer

INCI: PEG-400/1,4-Butanediol/SMDI Copolymer

A synthetic film former that helps makeup and sunscreen stay put longer, but may feel tight or heavy on some skin types.

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In plain English

This is a plastic-like polymer that forms a thin, flexible film on your skin or hair. It is commonly added to products like long-wear foundation, waterproof mascara, and sunscreen to help them resist water, sweat, and smudging. Think of it like a clear, invisible shield that holds the product in place. While it is generally safe and non-irritating, the film can sometimes feel a bit tight or heavy, especially if you have dry or sensitive skin.

Review score

Safety, usefulness, and evidence

3.5Good
3.5/ 5

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
How reviews are scored

Quick decision guide

Useful, but context matters

PEG-400/1,4-Butanediol/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.

  1. Step 1Start with the score, then check the irritation and clogging risk before judging PEG-400/1,4-Butanediol/SMDI Copolymer.
  2. Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
  3. 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

low

Less likely to sting, burn, or bother most users, though sensitive skin can still react.

Clogging risk

low

Less likely to feel heavy or contribute to clogged pores for most skin types.

Evidence level

moderate

There is useful support, but formula details and claim strength still matter.

What it is

A synthetic copolymer made from polyethylene glycol (PEG-400), 1,4-butanediol, and saturated methylene diphenyl diisocyanate (SMDI). It belongs to the polyurethane family and is engineered to form a durable, flexible film on surfaces.

How it works

When applied, the polymer chains spread out and then link together as the solvent (usually water or alcohol) evaporates. This creates a continuous, elastic film that physically locks in pigments, UV filters, or styling agents. The film is water-resistant but breathable enough to allow some moisture vapor to escape.

Pros

Excellent staying power

Creates a flexible film that helps makeup and sunscreen resist water, sweat, and rubbing, so you don't have to reapply as often.

Non-comedogenic for most

Unlikely to clog pores, making it a good option for acne-prone skin when used in non-greasy formulations.

Cons and cautions

Can feel tight or heavy

The film may cause a slight pulling sensation on dry skin, and some people find it feels like a mask.

Requires double cleansing

Water alone won't remove it; you'll need an oil-based cleanser or micellar water to break down the film, which can be inconvenient.

Best for

  • People who want long-lasting makeup or sunscreen
  • Those with oily or combination skin who need extra staying power

Use caution if

  • Individuals with very dry or dehydrated skin who dislike a tight feeling

Usage tips

Apply a hydrating moisturizer underneath to minimize any tight feeling.
Remove thoroughly with an oil-based cleanser or micellar water to avoid residue buildup.
Shake well before use if the product contains this polymer, as it can settle over time.

Safety summary

Generally considered safe for topical use. Low irritation and comedogenic potential. The main downside is the tight feeling it can cause on dry skin and the need for thorough removal.

Research notes

Limited independent studies on this specific copolymer, but the broader class of polyurethane film formers has been well-reviewed by cosmetic safety panels. No significant safety concerns have been identified at typical use levels.

Common label clues

Typical concentration
0.5% to 5% in leave-on products; up to 10% in rinse-off products
Regulatory status
Approved for use in cosmetics in the US, EU, and most other markets. The CIR panel has reviewed it and found it safe at concentrations up to 10% in leave-on products.
Common uses
Sunscreens, Long-wear foundations, Waterproof mascaras, Hair styling gels, Setting sprays
Environmental note
As a synthetic polymer, it is not biodegradable and may contribute to microplastic pollution. Some brands are moving toward biodegradable alternatives.

Good to know

  • This ingredient is often listed under trade names like 'Polyurethane-14' in some regions.
  • It is considered safe by the Cosmetic Ingredient Review (CIR) panel at typical use levels.
  • The 'PEG' part means it is water-soluble, but the film itself is water-resistant once dry.

Common questions

What is PEG-400/1,4-Butanediol/SMDI Copolymer in beauty products?

This is a plastic-like polymer that forms a thin, flexible film on your skin or hair. It is commonly added to products like long-wear foundation, waterproof mascara, and sunscreen to help them resist water, sweat, and smudging. Think of it like a clear, invisible shield that holds the product in place. While it is generally safe and non-irritating, the film can sometimes feel a bit tight or heavy, especially if you have dry or sensitive skin.

What does PEG-400/1,4-Butanediol/SMDI Copolymer do in a beauty product?

When applied, the polymer chains spread out and then link together as the solvent (usually water or alcohol) evaporates. This creates a continuous, elastic film that physically locks in pigments, UV filters, or styling agents. The film is water-resistant but breathable enough to allow some moisture vapor to escape.

Is PEG-400/1,4-Butanediol/SMDI Copolymer safe for most people?

Generally considered safe for topical use. Low irritation and comedogenic potential. The main downside is the tight feeling it can cause on dry skin and the need for thorough removal.

Who should be careful with PEG-400/1,4-Butanediol/SMDI Copolymer?

Individuals with very dry or dehydrated skin who dislike a tight feeling

Research sources

Cosmetic Ingredient Review (CIR) - Polyurethane PolymersOpenEuropean Chemicals Agency (ECHA) - PEG-400/1,4-Butanediol/SMDI CopolymerOpenPubMed - Safety of Film-Forming Polymers in CosmeticsOpen

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.