Looking at yourself in the mirror in the morning, you find that the inevitable has struck: your first gray hairs! Whether you’re in your 20s or 50s, gray hair is eventually catching up with us all.
When the cells that produce the pigments in our hair become too damaged, the next hair that grows is gray. During hair growth, melanocytes make pigment and pass it on to hair progenitor cells at the base of the hair follicle. These cells, in turn, transform into various components of growing hair. As our hair grows, pigments are continually incorporated, resulting in our unique hair color. The cells responsible for this process are the melanocytes which produce pigments at the base of the hair follicle.
In normal hair growth, the follicle produces hair at a rate of about 1 centimeter per month for several years. But all the cells of our body are damaged more and more during our life, and these melanocytes end up disappearing. When all the melanocytes are lost in a particular hair follicle, the next hair to grow will be gray or white. The biology of hair growth is quite complex, with a multitude of specialized cells involved in the structure and function of the hair follicle. Scientists continue to elucidate the process of human hair growth and pigmentation.
What controls pigmentation?
Humans have two different types of pigments. Eumelanin is responsible for black and brown colors, while pheomelanin is responsible for orange and yellow colors. Genes determine the mix of pigments each individual produces, which is why hair color is often similar within families. The exact mechanisms that control pigmentation are still unclear. However, recent research points to a finely tuned interaction between several hair follicle cells. Hair progenitor cells would release a protein called stem cell factor, which is essential for the production of pigments by melanocytes. In studies on mice, researchers have shown that if this protein is missing, hair color is lost. When the hair stops growing, the hair follicle undergoes significant structural changes and enters a period of rest. During this process, the melanocytes naturally die.
However, the melanocyte stem cells in the hair follicle normally produce a new set of reliable melanocyte sources at the start of the next hair growth cycle. Once new hair begins to grow, these melanocytes again provide pigmentation. But when melanocytes are damaged or absent, the hair that is produced lacks color and may appear gray or white.
Hair growth after damage
Human hair follicles that produce gray or white hair show higher levels of cell damage caused by free radicals. In these follicles, melanocytes and melanocyte stem cells are absent. In mice, when the DNA of hair follicle melanocyte stem cells was damaged Trusted source, it resulted in permanent cell damage. These stem cells were then unable to reproduce. Without the stem cell pool, the next cycle of hair growth takes place without melanocytes, resulting in gray hair.
Although it has not yet been possible to fully establish cause and effect in graying hair in humans, the accumulation of damage in melanocyte stem cells over time most likely leads to loss of this cell population. Each hair follicle will eventually be unable to produce colored hair. So, if it’s inevitable that we’ll all lose pigmentation in our hair one day, why do some of us turn gray in our 20s, while others retain their colored locks well into our 50s? Research from 2016 showed that people with a certain variant of the interferon regulatory factor 4 gene are prone to graying earlier.
As with many of our other traits, we can thank our parents for passing on their propensity for graying.
