What Gives Hair Its Color?
Put a single hair under a microscope, and you'll see granules of black, brown, yellow, or red pigment. What you are seeing are tiny particles of melanin, the same pigment that gives skin its color. Inside hair follicles, special cells called melanocytes produce melanin, which is deposited in the middle layer, or cortex, of the three-layered hair shaft. As the hair grows upward, pigment continues to form in the cells of the cortex. Some hair follicles make more pigment than others. Usually the hair of eyebrows is the darkest colored hair on the body.
In hair as in skin, there are two kinds of melanin. Eumelanin makes hair black or brown. Pheomelanin makes it red or blond. Only redheads--or those carrying the genes for red hair--make pheomelanin. Auburn-hair results from pheomelanin nearly hidden by eumelanin, and pheomelanin present in small amounts can make black hair shiny.
Pigment production changes with age. Often Caucasians who are blond in infancy produce darker hair as they grow older. The gray or white hair of old age results from a loss of activity in the melanocytes. In young people, an enzyme called tyrosinase breaks apart the amino acid tyrosine as an important step in the manufacture of melanin. As people get older, less of that enzyme is produced, so less melanin is made. Eventually, the hair shaft grows out with little, if any pigment in the cortex. What's left is the color keratin. Keratin is the main protein that forms the structure of the hair shaft. Keratin without melanin looks yellowish gray.
About the Author
Faith Brynie, Ph D
Faith Brynie holds a B.A. in Biology from West Virginia University and an M.A. and Ph.D in science curriculum and instruction from the University of Colorado. She writes books and articles on science and health topics for children, teens, and non-scientist adults. Some of her books have won awards, including two 'Best Book of the Year' citations from the American Association for the Advancement of Science.