When it comes to wigs, hair extensions and other hair enhancements, human hair is by far the most popular choice. Not only does it feel more natural, but when cared for correctly, quality human hair can last years. But where does the hair used in these products really come from?
A strand of human hair consists of 3 key layers; the cuticle, cortex and medulla. Each layer contains a unique combination of proteins and pigments. The most important pigment, called melanin, is produced by a special group of cells in the epidermis, the outermost layer of the hair follicle. Melanin is responsible for the color and texture of hair. People with more melanin have darker, thicker hair while those with less produce thinner, lighter strands.
Each hair follicle is responsible for growing one hair at a time and goes through a cycle of growth, rest and shedding every few months. The cycle is the same for all hair, even though hairs on different parts of the body grow at varying rates. For example, downy hairs that grow on the arms, legs and chest develop faster than the long, coarser hair that grows on the scalp.
The first type of hair to grow in humans is a thin, unpigmented layer of fine, slender filaments known as lanugo, which appears during the third or fourth month of fetal development and sheds prior to birth or shortly after. After lanugo, other more heavily pigmented hairs develop. These include the longer, coarser hairs of the scalp and genital regions as well as the thicker, more pigmented eyebrows and eyelashes. The latter two are separate types from the vellus hairs that cover most of the remainder of the body except the palms of the hands, soles of the feet and mucous membranes.
Hair is a valuable source of information about our ancestors. For example, in 2009, Lucinda Backwell of the University of Witwatersrand in South Africa and Instituto Superior de Estudios Sociales, CONICET in Argentina announced that she had discovered what appeared to be the oldest hair fossils ever found—human hairs preserved in fossilized hyena poop (or coprolites) from 200,000 years ago.
In addition to its visual appeal, hair is an incredible heat insulator and protects the scalp from the sun’s harmful rays. Hair also creates a barrier to help keep the sweat produced in hot weather from reaching the skin’s surface. The thicker and more tightly coiled the hair, the better it is at insulating.
As researchers continue to investigate what genes determine the texture and color of hair, they are discovering new things about this fascinating trait. For example, a new study has shown that genes related to the production of the neurotransmitter serotonin may play a role in hair growth and pigmentation. Researchers have also determined that the secretion of a protein called tyrosinase determines whether a person’s hair is black, brown or blond. Mutations in this gene can cause a neurodegenerative disease that has an indirect relation to hair color.