What is the difference between a permanent and a semi-permanent hair color?

The distinction between permanent and semi-permanent hair color primarily lies in their formulation and their effects on hair structure. Permanent hair color is designed to penetrate the hair shaft and alter its structure, allowing for a long-lasting change in color that can endure multiple washes. This process typically involves a chemical reaction that opens the hair cuticle and allows the dye to bond with the hair's cortex, resulting in colors that remain vibrant until the hair grows out or is cut.

In contrast, semi-permanent hair color does not change the hair structure. Instead, it coats the outside of the hair cuticle and typically washes out gradually over time, usually lasting between 4 to 12 shampoos depending on the specific product used and the hair's porosity. Because it does not penetrate the hair shaft, semi-permanent color is often used for temporary changes, enhancing existing color or adding shine without the commitment of a permanent color.

This clear distinction underlines why the statement about permanent color changing the hair structure while semi-permanent does not is accurate and represents the foundation for understanding different coloring processes and their implications for hair care and treatment.