Functional Actives
- Hair growth/Anti hair loss
Human skin has been calculated to carry approximately 5 million hair follicles, with the 100,000 hair follicles of the scalp (plus those of eyelashes and eyebrows) being most visible, and therefore psychosocially most important ones.
The function of scalp hair for humans is invested mostly in its value as a communication device or signal, and so together with epidermal pigmentation the hair fiber-for most of the phenotypic variation between different human subpopulations.
The progressive loss of visible hair during patterned balding results from the gradual transformation of terminal follicles, producing the long, thick, pigmented hairs of youth, to smaller vellus follicles forming short, colorless, virtually invisible vellus hairs. This is a major change in cell biological terms; follicles possess a unique mechanism, the hair follicle growth cycle, which allows these change. Each follicle normally undergoes a continual series of active, growing phases called anagen, alternating with periods of rest or telogen, which are separated at the end of anagen by a brief regression or catagen phase. (Figure 1)
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Figure 2.
Model of androgen action in the hair follicle
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This involves the destruction of the original lower follicle, and its total regeneration to from another follicle that can produce a totally new hair.
The original hair is lost via active shedding called exogen. In this way, the post-natal hair follicle appears to retain the ability to recapitulate the later stages of follicular embryogenesis throughout life. Among all androgens, dermal papilla cells are most affected by 5α-dihydrotestosterone (DHT). It is synthesized in these cells from testosterone under catalytic action of the enzyme 5α-reductase. (Figure 2)
Human hair growth can be distinguished from that in most other mammals by its rather mosaic pattern of hair follicle activity; we have all but lost our ability to grow hair synchronously or as a wave. Instead, each hair follicle has significant autonomy for growth and pigmentation. The hair bulb exhibits the body's second highest rate of cellular proliferation (after hematopoietic and intestine tissue), and can still produce functional fibers right up until our last and oldest days of life even if this extends beyond 12 decades.
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