Looking into the morning mirror, you see the unavoidable tragedy has hit: the first gray hair! If you’re in your 20s or 50s, gray hair finally catches up with us all.
Melanocytes produce pigment during hair growth and transfer it to progenitor hair cells at the base of hair follicle. In addition, these cells transform into the diverse components of growing hair.
When our hair grows, pigments are constantly added, resulting in our distinctive hair colour. 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 has been developing hair for many years at a rate of about 1 centimeter per month.
But throughout our lifetime, all the cells in our body are getting progressively damaged, and these melanocytes are inevitably lost. If all the melanocytes are lost in a specific hair follicle, gray or white will be the next hair that develops next.
The hair growth biology is very complex, with a host of different cells involved in the structure and function of hair follicles. Scientists continue to unravel the process of human hair growth and pigmentation.
What controls pigmentation?
Humans have two distinct pigment types. Eumelanin is responsible for black and brown colours, while orange and yellow are responsible for pheomelanine.
Genes decide the pigment mix that is created by each person, which is why hair color is often similar within families.
The exact mechanisms regulating pigmentation are still not clear. Recent research however, points to a finely tuned interplay in the hair follicle between many cells.
Hair progenitor cells are recorded to release a protein called stem cell factor, which is a prerequisite for melanocyte pigment production. The researchers have shown in mouse experiments that hair color is lost when this protein is absent.
The hair follicle undergoes drastic structural changes once the hair stops developing, and enters a time of rest. Melanocytes die, naturally, during this cycle.
Nonetheless, at the start of the next hair growth cycle melanocyte stem cells in the hair follicle usually develop a new collection of melanocytes.
When the new hair begins to develop, these melanocytes are again making sure there is pigmentation. But when the melanocytes get impaired or missing, the hair produced is lacking in color and can look gray or white.
Hair growth after damage
Research has shown that human hair follicles developing gray or white hair have higher rates of cellular damage that free radicals can cause. Melanocytes and stem cells from melanocytes are absent in certain follicles.
For mice, when melanocyte stem cell DNA was destroyed in the hair follicle, it resulted in irreversible damage to cells. Therefore, those stem cells do not replicate.
The next cycle of hair growth without the reservoir of stem cells continues without melanocytes, resulting in a gray head.
Though it has not yet been possible to completely identify cause and effect in humans during hair graying, the accumulation of damage in melanocyte stem cells over time most likely leads to a loss of this cell population. Eventually any hair follicle won’t be able to produce colored hair.
And, while it’s unavoidable that one day we’re all going to lose our hair pigment, why do some of us go gray in our 20s and some of us keep our bright locks until our 50s? Research from 2016 found that individuals with a certain version of the regulatory factor 4 interferon gene are vulnerable to earlier graying.
