How Does It Work? Hair Bleaching
An estimated one third of women over the age of 18 use some form of hair dye. As any bottle blonde knows, in order to get a lighter color of hair, one needs to use a bleaching agent. This post will explore the mechanism of hair bleaching.
|We’re gonna need some bleach.|
In order to learn how hair bleach works, we’ll first need to establish why some people have naturally blonde hair, whereas others have naturally dark hair.
There are two kinds of naturally occurring hair pigments: eumelanin and pheomelanin. Eumelanin is what gives hair a dark brown color. Pheomelanin is what gives red pigmentation. The molecules themselves may differ slightly, resulting in, for example, eumelanin that is brown as opposed to black. Low concentrations of both eumelanin and pheomelanin result in blonde hair.
Eumelanin and pheomelanin are long polymers. Because they are conjugated polymers, meaning they alternate between double and single carbon bonds, they are capable of absorbing light. Thus, they appear dark in color.
A quick chemistry reminder: a single bond is when two chemical elements are bound by a single pair of electrons. A double bond is when they are bound by two pairs of electrons.
The primary bleaching ingredient in hair dye is hydrogen peroxide. It is an oxidizing agent, meaning that it is capable of removing electrons from other molecules. Melanin molecules, with their numerous double bonds, have a few pairs of electrons to spare.
Hydrogen peroxide reacts with melanin, breaking their double bonds and eliminating their ability to absorb light. Because pheomelanin is more stable than eumelanin, hair that is in the process of being bleached often takes on an orange hue.
In addition to hydrogen peroxide, commercial bleaching products will usually have persulfate salts to help accelerate the process and stabilizers to help prevent the breakdown of hydrogen peroxide.
The brassy mid-bleach color is the result of pheomelanin.