Toning It Down: Brassiness Explained

What causes hair to look brassy over time?

It starts at the molecular level, and it's all about melanin. Your natural hair contains two types - eumelanin (the dark pigment) and pheomelanin (the warm gold, copper or red pigment). When we artificially lighten hair, we extract these pigments in stages. Eumelanin oxidizes more easily, while pheomelanin is more stubborn and harder to remove.

In the case of traditional highlight colors and blondes, colorists apply toners to cancel out the warmth that any residual pheomelanin leaves behind. Otherwise, they use developer (hydrogen peroxide) to lift the cuticle and allow color molecules to penetrate. Over time, these artificial pigments begin to slip out of the cuticle, and the tinier blue and violet color molecules escape more quickly than the warm, coppery ones.

Then there are environmental factors: UV light and chlorine both break down color molecules. Hard water deposits minerals like iron and copper on your hair, which then oxidize. All of these factors bring out any underlying warmth and brassiness.

What hair types are most prone to this and why?

Naturally dark hair that's been lightened is the most vulnerable. The darker your natural base, the more underlying warm pigments you have. When we lighten brunette hair, we're bringing those rich deposits of copper, red, and gold molecules to the pore.

Gray or white hair is prone to brassiness, too. It may have little natural pigment, but its fragile strands are more porous—and thus apt to absorb minerals and yellowing agents from styling products, sunlight, and even your natural scalp oils.

Fine hair types get brassy more quickly because the smaller diameter of each strand means fewer color molecules can be deposited during the coloring process. That gives the color less staying power – and since the cool tones fade faster, brassiness emerges sooner.

Highly porous hair, regardless of its natural color, is exceptionally prone to brassiness. When the cuticle layer is damaged from heat styling, chemical processing, or environmental factors, it's like a sieve that allows color molecules to escape unevenly. The larger warm pigments tend to stay trapped while the smaller cool ones slip away.

Curly and textured hair types often battle brassiness because they naturally have a more open cuticle layer. This inherent porosity allows color molecules to escape more easily. Plus, these hair types are typically drier, which accelerates color fading and emphasizes those underlying warm tones.