What does the term 'vehicle' refer to in cosmetic formulations?

In cosmetic formulations, the term 'vehicle' refers to a substance that acts as a medium for delivering other ingredients effectively. Vehicles are typically used to aid in the penetration and distribution of active ingredients on the skin or hair. They can include substances like oils, creams, lotions, or gels that carry active components to the desired area of application.

The role of a vehicle is crucial because it helps to ensure that the beneficial properties of the active ingredients can be absorbed and function optimally once applied. For example, in skincare products, the vehicle can influence how well the skin absorbs vitamins, acids, or moisturizers, enhancing the overall effectiveness of the formulation.

The other options do not accurately define 'vehicle' in this context. Methods of testing products pertain to quality assurance, enhancing color refers to color additives used for aesthetic purposes, and a type of preservative relates to ingredients that prevent microbial growth but not to the delivery of active ingredients.