Film-Forming Agent

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.

Polyquaternium-51 references

  • UL Prospector.com, accessed April 2023

Peer-reviewed, substantiated scientific research is used to assess ingredients in this dictionary. Regulations regarding constraints, permitted concentration levels and availability vary by country and region.

Ingredient ratings


Proven and supported by independent studies. Outstanding active ingredient for most skin types or concerns.


Necessary to improve a formula's texture, stability, or penetration.


Generally non-irritating but may have aesthetic, stability, or other issues that limit its usefulness.


There is a likelihood of irritation. Risk increases when combined with other problematic ingredients.


May cause irritation, inflammation, dryness, etc. May offer benefit in some capability but overall, proven to do more harm than good.


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Not Rated