Initially, hair is white. It gets its natural color from a type of pigment called melanin. The formation of melanin begins before birth. The natural color of our hair depends upon the distribution, type and amount of melanin in the middle layer of the hair shaft or cortex.
Hair has only two types of pigments: dark (eumelanin) and light (phaeomelanin). They blend together to make up the wide range of hair colors.
Melanin is made up of specialized pigment cells called melanocytes. They position themselves at the openings on the skin’s surface through which hair grows (follicles). Each hair grows from a single follicle.
The process of hair growth has three phases:
- Anagen: This is the active growth stage of the hair fiber and can last from 2- 7 years. At any given moment 80-85% of our hair is in the anagen phase.
- Catagen: Sometimes referred to as the transitional phase, which is when hair growth begins to “shut down” and stop activity. It generally lasts 10- 20 days.
- Telogen: This occurs when hair growth is completely at rest and the hair fiber falls out. At any given time, 10-15 % of our hair is in the telogen phase, which generally lasts 100 days for scalp hair. After the telogen phase, the hair growth process starts over again to the anagen phase.
As the hair is being formed, melanocytes inject pigment (melanin) into cells containing keratin. Keratin is the protein that makes up our hair, skin, and nails. Throughout the years, melanocyctes continue to inject pigment into the hair’s keratin, giving it a colorful hue.
We know that stress creates oxidative damage in the body, and it’s been linked to a lot of premature-aging syndromes. So it’s thought that the stress, that stress causes oxidative damage, which may cause damage to the melanocytes and may cause us to grow gray earlier. We know that smokers tend to go gray more so than the general population, and again it’s felt that it’s probably due to the oxidative damage that smoke causes and how it affects the pigment-producing cells in the hair. I think eating a well-balanced diet, so you make sure that you don’t develop any nutritional deficiencies, that’s another thing that can be done. And modulating your stress. That’s another thing you have control over, which over time can cause oxidative damage and, again, make you prone to potentially more gray hair.
With age comes a reduction of melanin. The hair turns gray and eventually white.
Pigmentation of mammalian hairs is mediated by specialized pigment-producing cells referred as melanocytes. Hair pigmentation is tightly linked with hair regeneration cycles, where melanocytes proliferate and differentiate during the hair growth phase, but depleted by apoptosis during the regression phase.
This periodical appearance of melanocytes is maintained by a small pool of immature stem cells residing in the hair follicle. Melanocyte stem cells offer an advantageous model by which to elucidate molecular basis of stem cell regulation, since genetic alterations affecting melanocyte regulation result in visible and yet viable phenotypes.
Hence, by integrating melanocyte-specific in vivo gene manipulation approach and the subsequent phenotype analysis, melanocyte stem cell system provide an irresistible clue to identify key molecules for the stem cell regulation. Consolidation of such data would ultimately reveal an entire molecular network underlying the regulation of stem cells, which would not only contribute complete understanding of stem cell biology, but also provide valuable insights into medical application of stem cells.