What aids the small colorless molecules in permanent hair color to enter the hair?

The small colorless molecules in permanent hair color are designed to penetrate the hair shaft, and an alkaline substance plays a crucial role in facilitating this process. When hair is treated with an alkaline substance, it causes the hair's cuticle layer to swell and open up, making it more permeable. This allows the small color molecules to effectively enter the hair cortex where they can react with the dye precursors to develop the final color.

Alkaline substances also help to raise the pH level of the hair and the surrounding environment, which is essential for the chemical reactions that lead to the permanent change in hair color. This transformation is a key feature of permanent hair color, as the color is meant to be long-lasting and resistant to washing out.