A nonoxidative process that allows small colour molecules to penetrate the cuticle and enter the cortex is known as what?

The correct choice is semi-permanent, as it describes a nonoxidative coloring process that utilizes smaller color molecules that can penetrate the hair cuticle and reach the cortex. This type of coloring does not require a developer or lightener, which distinguishes it from oxidative and permanent methods. The color results are less long-lasting than permanent dyes, typically fading after a number of washes, typically 4 to 12 shampoos, due to the nature of the pigments involved.

In contrast, oxidative coloring requires a chemical reaction that involves a developer, which results in longer-lasting color by creating larger molecules that bond more permanently within the hair shaft. Permanent processes also involve the same oxidation reaction that changes the hair structure for lasting results. Temporary hair colors, on the other hand, usually coat the outside of the hair rather than penetrating the cuticle, making them easy to wash out without altering the hair structure. Semi-permanent coloring strikes a balance, providing more longevity than temporary hues while remaining nonoxidative.