Quick answer

Synthetic polymer with a large molecular structure; Has humectant and film-forming properties for skin and hair; Meshes well with lipids found in skin’s surface layers; Considered safe as used in cosmetics Key benefits: Hydration.

Polyquaternium-51

Updated

2-(N,N,N-Trimethylamino)ethyl 2-(2-methyl-2-propenoyloxy)ethyl phosphate inner salt, polymer with butyl 2-methyl-2-propenoate

Purpose

Synthetic quaternary compound whose role in cosmetics is humectant and film-forming agent, where it helps ingredients adhere better to skin.

Rating

GOOD

Category

Film-Forming Agent, Humectant

INCI Purpose

FILM FORMING, SKIN CONDITIONING

Benefits

Hydration — Attracts and locks in moisture to keep skin plump and dewy

Alternative Names

Hair Profile

Functions

Conditioning Film Former

At a Glance

Synthetic polymer with a large molecular structure

Has humectant and film-forming properties for skin and hair

Meshes well with lipids found in skin’s surface layers

Considered safe as used in cosmetics

Article

Polyquaternium-51 is a synthetic, polymeric quaternary ammonium compound, which means it’s a large molecule whose unique amphiphilic (water- and oil-loving properties) structure has a charge which gives it conditioning and film-forming properties for skin and hair.

Its humectant properties are due to its structural similarity to lipids found in the corneocytes (surface cells) of human skin. As such, it works to preserve skin’s barrier and help prevent water loss.

Usage levels of polyquaternium-51 in skin care typically range from 0.5–5%, with concentrations of 2­–5% most often used in rinse-out hair care products such as conditioners. Much lower amounts, such as 0.021%–0.05%, may be used in products such as eye makeup or 0.02% in moisturizers. A formal safety assessment hasn’t been published, although a draft report exists that which doesn’t indicate polyquaternium-51 poses a risk to skin in amounts currently used.

See: Polyquaterniums, Quaternary Ammonium Compounds, Polymer

References