What is the primary ingredient in most shampoos?

The primary ingredient in most shampoos is deionized water. It serves as the base for the product and allows for the even distribution of other ingredients. The presence of water is essential as it helps to solubilize and disperse the surfactants and other functional agents present in the formulation. Water also makes the shampoo easy to apply and rinse out, which is crucial for effective cleansing.

While sodium lauryl sulfate and cocamidopropyl betaine are important active ingredients used for their cleansing and foaming properties, they are not the primary components by volume in shampoos. These surfactants are typically included in smaller quantities compared to the overall formulation. Fragrance, while significant for user experience and scent, also does not constitute the primary volume of shampoo's formulation. Therefore, deionized water is correctly identified as the primary ingredient, functioning as the foundation for the product.