Polyquaternium-51
Reviewed by Daisy · Last updated 18 Aug 2026
Synthetic polymer with a large molecular structure | Has humectant and film-forming properties for skin and hair
Addresses
EWG Safety Score
What Is Polyquaternium-51?
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.
Benefits for Your Skin
Clinical Evidence & References
Published Research
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UL Prospector.com, accessed April 2023 [URL Not Found]
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International Journal of Cosmetic Science, August 2009, pages 271–277 [URL Not Found]
From the Clinic
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