Ingredient review

Dimethicone/Mercaptopropyl Methicone Copolymer

INCI: DIMETHICONE/MERCAPTOPROPYL METHICONE COPOLYMER

A silicone film former that helps products resist water and last longer, but may feel heavy on fine hair or oily skin.

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In plain English

This is a type of silicone that forms a flexible, water-resistant layer on your skin or hair. It helps makeup stay put longer and keeps hair styles in place, even in humidity. Because it's a large molecule, it sits on the surface rather than penetrating, so it's generally non-irritating. However, it can feel a bit heavy or cause buildup if you use it daily without proper cleansing.

Review score

Safety, usefulness, and evidence

3.8Good
3.8/ 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

Dimethicone/Mercaptopropyl Methicone 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 Dimethicone/Mercaptopropyl Methicone 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 silicone copolymer that combines dimethicone (a common smoothing silicone) with a mercaptopropyl group, which gives it extra water-repelling and film-forming abilities. It is designed to create a durable, flexible coating on surfaces.

How it works

When applied, the copolymer spreads into a thin, even film that dries to form a water-resistant barrier. This film helps lock in other ingredients, prevents moisture from weakening the product, and provides a smooth, non-tacky feel. On hair, it can help hold curls or styles by coating each strand.

Pros

Excellent water resistance

Helps mascara, eyeliner, and foundation stay put through sweat, tears, and humidity, reducing the need for touch-ups.

Smooth, non-tacky finish

Unlike some sticky film formers, this silicone leaves a silky, comfortable feel on skin and hair without a heavy residue.

Cons and cautions

Potential buildup

Because it forms a durable film, it can accumulate on hair or skin over time, requiring double cleansing or a clarifying shampoo to remove completely.

Environmental persistence

As a silicone-based polymer, it is not readily biodegradable and may contribute to microplastic pollution in waterways.

Best for

  • People who want long-lasting, waterproof makeup
  • Those with thick or coarse hair looking for hold and frizz control

Use caution if

  • Those with very fine or easily weighed-down hair
  • People who prefer water-soluble, easy-to-remove formulas

Usage tips

Use an oil-based cleanser or micellar water to fully remove products containing this ingredient.
If using in hair products, alternate with a clarifying shampoo once a week to prevent buildup.
Apply in thin layers for best results—too much can feel heavy or cause flaking.

Safety summary

Considered safe for topical use in cosmetics at typical concentrations. Low irritation and comedogenic risk. No known systemic toxicity from dermal exposure. However, like all silicones, it may cause buildup and is not environmentally friendly.

Research notes

Limited peer-reviewed studies specifically on this copolymer, but its components (dimethicone and related silicones) have been extensively reviewed by the Cosmetic Ingredient Review (CIR) panel and found safe for use. The film-forming and water-resistant properties are well-documented in cosmetic science literature.

Common label clues

Typical concentration
0.5% to 5%
Regulatory status
Approved for use in cosmetics in the US (FDA), EU (CosIng), and many other regions. No specific concentration limits are set, but it is generally used at low levels.
Common uses
Waterproof mascaras, Long-wear foundations, Hair styling products, Sunscreens
Environmental note
As a silicone polymer, it is not biodegradable and may persist in the environment. Some manufacturers are exploring bio-based or biodegradable alternatives.

Good to know

  • This ingredient is often found in 'waterproof' or 'long-wear' labeled cosmetics.
  • It is considered safe for use in cosmetics by major regulatory bodies at typical concentrations.
  • On ingredient labels, it may appear near the end of the list because it is used in small amounts.

Common questions

What is Dimethicone/Mercaptopropyl Methicone Copolymer in beauty products?

This is a type of silicone that forms a flexible, water-resistant layer on your skin or hair. It helps makeup stay put longer and keeps hair styles in place, even in humidity. Because it's a large molecule, it sits on the surface rather than penetrating, so it's generally non-irritating. However, it can feel a bit heavy or cause buildup if you use it daily without proper cleansing.

What does Dimethicone/Mercaptopropyl Methicone Copolymer do in a beauty product?

When applied, the copolymer spreads into a thin, even film that dries to form a water-resistant barrier. This film helps lock in other ingredients, prevents moisture from weakening the product, and provides a smooth, non-tacky feel. On hair, it can help hold curls or styles by coating each strand.

Is Dimethicone/Mercaptopropyl Methicone Copolymer safe for most people?

Considered safe for topical use in cosmetics at typical concentrations. Low irritation and comedogenic risk. No known systemic toxicity from dermal exposure. However, like all silicones, it may cause buildup and is not environmentally friendly.

Who should be careful with Dimethicone/Mercaptopropyl Methicone Copolymer?

Those with very fine or easily weighed-down hair People who prefer water-soluble, easy-to-remove formulas

Research sources

Cosmetic Ingredient Review (CIR) - Safety Assessment of Dimethicone and Related PolymersOpenPubChem - Dimethicone/Mercaptopropyl Methicone CopolymerOpenEuropean Chemicals Agency (ECHA) - Siloxanes and SiliconesOpen

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.