Common Name(s): Poloxamer 251,poloxamer (peo-ppo-peo triblock copolymer),steric polymeric emulsifier

CAS Number: N/a

DESCRIPTION

What It Does: Poloxamer 251 stabilises oil-in-water emulsions, solubilises fragrance oils and lipophilic actives in aqueous formulations, and provides steric foam stabilisation that remains effective across a broad ph and ionic strength range where charge-based emulsifiers fail. at concentrations above its critical micelle concentration, it forms spherical or worm-like micelles that encapsulate lipophilic materials for transparent clear-gel or microemulsion delivery.

Why It's Used: Formulators choose poloxamer 251 because it provides emulsion stability through steric mechanisms rather than electrostatic charge — meaning performance is maintained at high salt concentrations, across the full cosmetic ph range, and at elevated temperatures where many ionic emulsifiers destabilise. its pharmaceutical gras status and extensive toxicological documentation (used intravenously in pharmaceutical drug delivery) provides the highest possible safety assurance. the peo-ppo-peo architecture also enables temperature-responsive gelation useful in certain drug delivery and sensory-enhancing cosmetic applications.

How It Works: Poloxamer 251 functions through steric emulsion stabilisation: the peo chains adsorb at oil-water interfaces with the ppo block anchored in the oil phase and peo chains extending into the water phase forming a dense polymer brush corona around emulsion droplets. when two droplets approach each other, their peo brush layers overlap — the loss of conformational entropy of the compressed chains creates a repulsive free energy barrier (steric repulsion) that prevents droplet coalescence. this entropic repulsion force operates independently of ph, ionic strength, and temperature, making steric stabilisation far more robust than electrostatic stabilisation. above the cloud point temperature, ppo blocks dehydrate, driving temperature-responsive micelle formation and gelation.

Typically Found In: Pharmaceutical-grade emulsions,microemulsions,temperature-responsive gels

TECHNICAL DETAILS

Primary Category: Active ingredient – cosmetic active

Secondary Functions: Skin conditioning

Application Areas:

Typical Concentration Range: 1%–20%

SOURCING & ETHICS

Vegan Status: Conditional - supplier confirmation required

Halal Status: Unverified - supplier confirmation required

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier. [audit 2026-07-29 rev2: the record's own source_notes does not assert a non-animal origin, or instructs the reader to verify with the supplier; "yes" asserts knowledge the record does not hold. determination requires shariah-panel sign-off.]

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Good safety profile at recommended concentrations. ewg score: 1–2.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Poloxamer steric vs electrostatic stabilisation robustness: electrostatic stabilisers (sds, cetrimide) require a charged double layer that collapses at high ionic strength (debye screening) or extreme ph. steric stabilisers like poloxamer 251 use polymer entropy — compression of peo brush chains creates an osmotic pressure difference independent of ionic environment. at 1m nacl where many ionic emulsions break, poloxamer-stabilised emulsions remain stable from the salt-independent entropic repulsion mechanism.

Last Verified: 2026-03-12

Primary Sources: Cosing database,poloxamer 251 poloxamer pharmaceutical cosmetic review