Polyquaternium-37 (PQ-37) is a widely used, synthetic polymer found in personal care and cosmetic products. This ingredient functions primarily as a conditioning agent and thickener, forming a key component in hair conditioners and skin lotions. It belongs to a larger family of compounds known for their ability to modify product texture and improve the feel of hair and skin.
Chemical Composition and Properties
Polyquaternium-37 is classified as a polycationic polymer, meaning it is a large molecule with multiple sites carrying a positive electrical charge. This positive charge is the foundation of its functionality. The structure is based on an acrylic homopolymer backbone, making it a synthetic compound.
The polymer’s mechanism relies on simple electrostatic attraction. Hair and skin surfaces, particularly when damaged, typically carry a slight negative charge. The positive charges along the PQ-37 chain are drawn to these negative sites, allowing the polymer to adhere effectively to the surface of the hair shaft or skin. This binding creates a uniform, ultra-thin film.
This film-forming capability contributes to its physical properties, which include water-insolubility once dried and an ability to modify the flow of liquids. Its efficiency allows it to work effectively at low concentrations, delivering textural and functional changes to the final product.
Primary Roles in Cosmetic Formulations
Polyquaternium-37 performs three distinct functions within cosmetic formulations.
Conditioning Agent
The most recognized role is its performance as a conditioning agent in hair care products. By neutralizing the negative static charge on the hair surface, it reduces flyaways and frizz. The polymer bonds ionically to the keratin, smoothing the cuticle. This results in improved wet and dry detangling, enhanced hair alignment, and increased shine.
Thickener (Rheology Modifier)
Its second function is as a thickener, or rheology modifier, which dictates the texture and consistency of the product. The polymer increases the viscosity of the formulation, helping to stabilize the product texture and provide a cushiony feel. This property allows formulators to create rich creams, lotions, and gels that maintain their structure. Its ability to thicken is often cold-processable, which simplifies manufacturing processes.
Emulsion Stabilizer
The third primary role is that of an emulsion stabilizer. Many personal care products are emulsions, which are mixtures of oil and water that naturally want to separate. PQ-37 helps to prevent this separation, ensuring that the oil and water phases remain uniformly distributed throughout the product. This stabilization is crucial for the shelf life and consistent application of complex formulations.
Safety Profile and Regulatory Status
Polyquaternium-37 is considered a low-hazard ingredient when used within established concentration limits. The Cosmetic Ingredient Review (CIR) Expert Panel has assessed the ingredient. It is formulated at low concentrations, often 0.2% to 2% active polymer, to be non-irritating to the skin and eyes.
Major regulatory bodies worldwide, including those in the United States and the European Union, permit its use, subject to concentration restrictions. These approvals are based on safety data that show minimal risk of toxicity or adverse reactions with normal use. The polymer’s large molecular size means it adheres to the surface of the skin and hair, minimizing the potential for systemic absorption.
A primary environmental consideration for PQ-37 is its synthetic nature and potential for persistence. As a synthetic polymer, it is not readily biodegradable. This raises concerns about its long-term accumulation in the environment following wash-off and wastewater treatment. This characteristic is common among many synthetic polymers used in consumer products.