Why you cannot do laser hair removal on light blond, white and red hair.

We are constantly bombarded by manufacturers and sales people telling us that their laser or light-based equipment can do permanent hair removal on all hair colours. But as those of us with a bit of experience know by now, this is not the full truth.

So why can’t we treat some lighter hair colour?
Let’s start by looking at the science behind laser hair removal. A light pulse (laser / LED / IPL) is used to generate heat in the hair itself. Heat is created when the light is absorbed by eumelanin molecules that convert the light energy into heat energy. This heat then has to spread to the surrounding tissue, and for hair removal it is at the bottom of the follicle. It is also only during the active growing phase, anagen phase, that the dermal papilla is “embrace” by the hair root to such extent that you will create enough heat to kill the dermal papilla.

Lighter hair have less eumelanin and at a certain point the eumelanin density is not enough to generate enough heat to destroy surrounding tissue. This is the case with light blond hair.

Gray hair have very few eumelanin molecules spread throughout the hair to such extent that it will not cause any significant heat generation. White hair contains no eumelanin.

Red hair on the other hand contain a high density of melanin, but not eumelanin. The red colour comes from the presence of pheomelanin, a red-yellow pigment. It is very rare that you will encounter a mixture of eumelanin and pheomelanin in the same hair. Since most lasers and light-based devices for hair removal irradiate light in the red and infrared range, most of the energy is reflected by pheomelanin. Thus, no significant heat generation can take place for permanent hair removal.