Polyquaternium-51 Good Film-Forming Agent Hydration Polyquaternium-51 at a glance Synthetic polymer similar to phospholipids in skin’s outermost layer Offer humectant and film-forming benefits Contributes to the sensory aspects of cosmetics Amounts used in cosmetics are considered safe Polyquaternium-51 description Polyquaternium-51 is a synthetic polymer with film-forming and humectant benefits. Its moisture-binding properties stem from it being similar to the phospholipids found in fully mature skin cells known as corneocytes, found on skin’s surface layer. This ingredient’s very high molecular weight keeps it from penetrating past skin’s surface, but that’s OK since it works in this area to help skin maintain its moisture balance and prevent water loss. Polyquaternium-51 can provide elegant sensory properties to cosmetics, including hair care, as well as help key ingredients adhere better. Its safety has been evaluated but, at the time of this writing, has not been finalized. Typical usage levels of polyquaternium-51 in cosmetics is between 0.5–5%. These amounts (as well as greater concentrations) are considered non-sensitizing and non-irritating to skin. Related ingredients: Polyquaterniums Quaternary Ammonium Compounds Polymer