Polyquaternium-7 is a synthetic, water-soluble polymer utilized extensively across the personal care and cosmetic industries. This compound is incorporated into a vast array of products, from hair care to bath and body formulations. Its primary function is to modify the texture and appearance of hair and skin, providing conditioning benefits. It is typically supplied as a clear or pale yellow liquid for easy integration into manufacturing processes.
Chemical Classification and Structure
Polyquaternium-7 belongs to the polyquaternium group, which are polymers containing a positively charged nitrogen atom, classifying them as quaternary ammonium compounds or “quats.” The term “polymer” indicates a large molecule composed of many repeating smaller units, or monomers, linked together in a long chain. Specifically, Polyquaternium-7 is a copolymer built from two different types of monomers: acrylamide and diallyldimethylammonium chloride (DADMAC).
The designation “Polyquaternium-7” is a nomenclature assigned by the Personal Care Products Council to distinguish this specific structure from other polyquaternium compounds. The positive electrical charge, or cationic nature, of the DADMAC unit remains constant regardless of the product’s pH. This inherent positive charge dictates how the molecule interacts with the negatively charged surfaces of hair and skin.
Function as a Cosmetic Conditioning Agent
The strong conditioning capabilities of Polyquaternium-7 stem directly from its cationic charge and large polymer structure. Human hair and skin, especially when damaged or wet, possess a net negative charge due to proteins like keratin. The positively charged polymer is strongly attracted to these negatively charged sites, leading to electrostatic adsorption onto the surface of the hair shaft or skin layer.
This binding mechanism allows the polymer to deposit a thin, smooth, and continuous film on the surface. The film-forming property is responsible for several noticeable effects, including increasing the hair’s “slip,” which makes it easier to detangle and comb, particularly when wet. By smoothing the hair cuticle, the deposited layer also enhances light reflection, resulting in a shinier appearance and a softer feel.
The polymer’s positive charge neutralizes the static electricity that commonly builds up on hair, which is the mechanism behind its anti-static and frizz-reducing properties. This ingredient is highly effective even when used in surfactant-based products like shampoos and body washes, where it counteracts the drying effects of cleansing agents. It is a common component in two-in-one shampoos, rinse-off and leave-in conditioners, and body cleansers, where it provides lubricity and moisture retention.
Safety Profile and Environmental Impact
Polyquaternium-7 is widely regarded as safe for use in cosmetic and personal care products at the concentrations typically found in consumer goods. The Cosmetic Ingredient Review (CIR) Expert Panel, an independent scientific body, has evaluated the available data and concluded that the ingredient is safe as used. Studies indicate that it is not a dermal irritant or sensitizer at relevant concentrations, though minor, temporary eye irritation has been observed in testing.
A common concern involves trace amounts of the unreacted monomer acrylamide, which is a potential impurity. Reputable manufacturers ensure that the level of residual acrylamide is extremely low. This low level is generally considered to be of no toxicological significance when the final product concentration of the polymer is 5% or less. Like all cationic polymers, Polyquaternium-7 can contribute to product buildup on hair over time, which may require the use of clarifying products to remove.
The environmental fate of Polyquaternium-7 is a subject of discussion due to its persistent nature. As a synthetic polymer, it is not readily biodegradable, and at high concentrations, it may be harmful to aquatic life. In wastewater treatment plants, the positive charge of the polymer causes it to strongly adsorb to negatively charged sludge particles. While this process removes the substance from the water effluent, the compound accumulates in the sewage sludge, which may be used in agricultural applications or disposed of in landfills.