A review of the etiologies, clinical characteristics, and treatment of canities

Abstract

Hair pigmentation is regulated by follicular melanogenesis, in which the process consists of melanin formation and transfer to keratinocytes in the hair shaft. Human hair follicles contain two types of melanin: the brown‐black eumelanin and yellow‐red pheomelanin. Eumelanin is commonly present in black and brown hair while pheomelanin is found in auburn and blonde hair. Hair follicle melanogenesis is under cyclical control and is concurrently coupled to hair growth. Many factors including intrinsic and extrinsic factors affect the follicular melanogenesis. Though many studies have been conducted to identify the pathogenesis and regulation of hair pigmentation, the etiology of canities and hair pigmentation is still unclear. The pathogenesis of canities or gray hair is believed to occur either from insufficient melanin formation due to melanocyte degeneration or a defect in melanosomal transfer. Canities is an aging sign which often interferes with one's socio‐cultural adjustment. On the other hand, premature canities correlate with diseases such as osteopenia and cardiovascular disease. Risk factors associated with canities are not only genetic but also external causes. For example, smoking, alcohol consumption, and stress are among the most common factors. Camouflage techniques are still used as the primary treatment of canities. Further treatments for canities are being developed to achieve the true reversal of hair pigmentation.

Global Repigmentation Strategy of Grey Hair Follicles by Targeting Oxidative Stress and Stem Cells Protection

“…We also confirmed the results obtained by Tang and colleagues, by showing that the genes encoding for melanosome formation and transfer (CTNS, HPS5, MLPH, SLC24A5) were disturbed with oxidative stress, especially MYO5A [1,14]. Unfortunately, we did not find any significant modulation of KIT or Bcl-2 or Pmel17/gp-100, which are widely described as essential in human hair pigmentation [1,2,11,19,25].…”

“…Chronological ageing is well described today and the main cause is oxidative stress [19]. This stress is triggered by external and internal factors, such as UV, pollution, chemicals, cigarette smoke and psycho-emotional stress [9,20].…”

Investigation of the molecular signature of greying hair shafts

“…Canitie corresponds to a hair discoloration from grey to white. Hair ageing comprises weathering of the hair shaft [1] and ageing of the hair follicle [2]. The hair is composed of two anatomically distinct structures: the hair shaft, visible part above the surface of the skin, and the hair follicle, which is the subcutaneous part.…”

“…Greying has been largely investigated at the hair follicle level. Enzymatic reactions required for melanin synthesis as well as environmental factors such as ultraviolet radiation and pollution generate large quantities of reactive oxygen species (ROS), including hydrogen peroxide (H 2 O 2 ) [1, 11, 12]. Numerous studies have pointed out the weakening of the antioxidant system and the progressive accumulation of ROS, in particular H 2 O 2 in grey hair follicles [11, 13–17].…”

“…A study from Wood and collaborators investigated in vivo grey and white hair shafts at the molecular level by Raman microspectroscopy and revealed an accumulation of H 2 O 2 resulting in amino acids oxidation such as methionine and consequently affecting the activity of enzymes involved in melanogenesis [18]. Some publications highlight that greying hair become thin, brittle, dull, less manageable and are usually hard to stain [1, 12, 19, 20]. These observations may be due to changes in hair fibres structure occurring in the course of greying.…”