Polyquaternium-51 Bon Agent filmogène Hydratation Polyquaternium-51 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 Polyquaternium-51 description 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. Related ingredients: Polyquaterniums Quaternary Ammonium Compounds Polymer