Skin and hair play a major role in a person’s appearance. The colour of human hair – such as black, brown, blonde etc. – depends on the type of melanin in human hair follicles and its transformation from melanocyte to keratinocyte i.e. melanogenesis. As one grows older, melanocytes, the pigment cells in the hair follicles, die slowly; due to which, hair may not contain as much melanin as needed to maintain its color, and as a result, it turns grey, silver, or white. Greying of hair (also called canities) is no longer associated with age, and depends on several factors such as deficiency of vitamin B12, stress, smoking, genetics, and auto-immune diseases such as vitiligo and alopecia areata etc. Reversal of greying of hair is now receiving the attention of researchers worldwide.
MECHANISM OF HAIR GREYING
The process of hair growth consists of 3 phases;
- Anagen, the active growth stage of the hair fiber
- Catagen, wherein hair growth slows down
- Telogen, wherein hair growth completely stops and the hair fiber falls off
When hair is formed, melanocytes inject melanin into cells containing keratin, the basic structural protein of hair fibre, resulting in hair retaining its original colour. Melanogenesis, a process of melanin production and distribution, is reported to be controlled by neuroendocrine factors such as alpha melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH), ß-endorphin, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH)], and micropthalmia-associated transcription factor (MITF). Greying of hair is caused either by active hair growth; which induces oxidative or genotoxic stress in hair bulge, resulting in depletion of melanocyte stem cells (MSC); or dysfunction of melanocyte stem cells in the bulge, which in turn may be attributed to the generation of toxic reactive oxygen species (ROS) on melanocyte nuclei and mitochondria.