Silicone Quaternium-18

Silicone Quaternium-18 is a positively charged silicone polymer—a synthetic ingredient derived from silicone that has been modified with a quaternary ammonium salt. This modification allows it to bond to hair and skin surfaces, where it deposits a thin, conditioning film.In skincare, it functions primarily as an emollient and conditioning agent, though it appears in relatively few formulations (approximately 0.1% of skincare products). It is more commonly found in haircare products.

Silicone Quaternium-18 is cationic (positively charged), which allows it to electrostatically bind to the negatively charged surface of skin and hair. Once deposited, it forms a thin, invisible layer that smooths the outer texture and reduces friction between the skin surface and the environment.This film also acts as a mild moisture barrier, slowing water evaporation from the skin without fully occluding the surface—a property that makes it useful in light moisturisers and conditioning products.

This ingredient is typically used as a supporting agent rather than a primary active. It is most effective when formulated in products designed for daily use, such as lightweight moisturisers, serums, or conditioning treatments. Allow any product containing it to fully absorb before layering additional products.

Silicone Quaternium-18 is well-tolerated by most skin types and has a strong safety history in cosmetics. Some individuals sensitive to silicones may prefer silicone-free alternatives.