Let’s Not Split Hairs

What am I looking at?

This is an image of two human hairs being viewed under polarized light.

Biology in the background

Human hair comes in many different colors and textures. However, the basic structure of all hair is similar, with a few factors contributing to the visible differences. All hair is composed of keratin, a protein that also makes up our fingernails and the hooves and claws of other mammals. This fibrous protein links together to form strands (in the case of hair) or plates (in the case of fingernails, claws, etc.).

Differences in hair color are determined by a pigment called melanin, which is the same pigment that determines our skin color. Melanin is produced by cells called melanocytes, which are present in hair follicles and throughout the rest of our skin. There are two types of melanin that determine hair color: eumelanin and pheomelanin. Eumelanin is a brown/black pigment that results in brown or black hair (like the strand labeled 1). Pheomelanin is a red/yellow pigment; high concentrations of pheomelanin make hair look red. Blonde hair is the result of very low levels of brown melanin in the hair (like the strand labeled 2).

The texture of hair (curly versus straight) is determined by the shape and structure of the hair follicle (a curly follicle versus a straight follicle), among other factors.

Human hair can vary in thickness, but the average width of a strand is roughly 75 micrometers.

Technique

This image was created using a form of light microscopy called cross-polarization illumination.