What distinguishes permanent hair color from temporary hair color?

Permanent hair color fundamentally alters the hair's structure by penetrating the hair shaft and modifying its natural pigment. This chemical process typically involves a developer that opens the hair cuticle, allowing the color molecules to enter the cortex, where they bond with the existing color. This is why permanent hair color provides long-lasting results, often enduring until the hair grows out or is cut away.

In contrast, temporary hair color usually coats the outer layer of the hair and is designed to wash out after a few shampoos. Therefore, while temporary options provide a quick change, they do not change the underlying structure or produce long-lasting results like permanent hair color does.