The Complete Handbook of Hair Color

Chapter 1: Understanding Hair Color

Hair color is not paint. It does not sit on top of the hair shaft and wash away after a few weeks, nor does it require the hair to be a blank canvas before it can be applied. Instead, hair color is a chemical treatment that penetrates and alters the protein structure of the hair itself, either by depositing new pigment molecules into that structure or by lightening existing pigment through oxidation. Understanding what hair color actually is—and how it works chemically—is the foundation for every decision a professional, business operator, or serious hobbyist makes about which product to use, how to apply it, why it succeeds or fails, and where opportunity exists.

The Hair Shaft: What Color Targets

Hair is made of three layers: the cuticle (outer protective layer of overlapping scales), the cortex (middle layer containing proteins and natural pigment), and the medulla (innermost core, not always present and not the focus of color treatment). Natural hair color is produced by melanin—two types, eumelanin (brown and yellow pigments) and pheomelanin (red and yellow pigments)—which sits in the cortex. The ratio of these two melanins, plus their concentration and oxidation state, determines the shade you see.

The cuticle's overlapping scales act as a barrier. They lie flat when the hair is undamaged and closed, protecting the cortex. When the cuticle is raised—through alkaline conditions, heat, or mechanical manipulation—the scales lift, allowing molecules to penetrate into the cortex and allowing water and product to escape.