Human hair pigmentation – biological aspects

Abstract

Synopsis Skin and hair colour contribute significantly to our overall visual appearance and to social/sexual communication. Despite their shared origins in the embryologic neural crest, the hair follicle and epidermal pigmentary units occupy distinct, although open, cutaneous compartments. They can be distinguished principally on the basis of the former’s stringent coupling to the hair growth cycle compared with the latter’s continuous melanogenesis. The biosynthesis of melanin and its subsequent transfer from melanocyte to hair bulb keratinocytes depend on the availability of melanin precursors and on a raft of signal transduction pathways that are both highly complex and commonly redundant. These signalling pathways can be both dependent and independent of receptors, act through auto‐, para‐ or intracrine mechanisms and can be modified by hormonal signals. Despite many shared features, follicular melanocytes appear to be more sensitive than epidermal melanocytes to ageing influences. This can be seen most dramatically in hair greying/canities and this is likely to reflect significant differences in the epidermal and follicular microenvironments. The hair follicle pigmentary unit may also serve as an important environmental sensor, whereby hair pigment contributes to the rapid excretion of heavy metals, chemicals and toxins from the body by their selective binding to melanin; rendering the hair fibre a useful barometer of exposures. The recent availability of advanced cell culture methodologies for isolated hair follicle melanocytes and for intact anagen hair follicle organ culture should provide the research tools necessary to elucidate the regulatory mechanisms of hair follicle pigmentation. In the longer term, it may be feasible to develop hair colour modifiers of a biological nature to accompany those based on chemicals.

Bone morphogenetic proteins differentially regulate pigmentation in human skin cells

“…This subpopulation of neural crestderived cells migrates during embryogenesis to the epidermis and hair follicles and subsequently synthesize and distribute melanin to surrounding keratinocytes (KC) (Van Den Bossche et al, 2006;Tobin, 2008). Adequate pigmentation of skin is dependent upon successful transport and transfer of a unique membrane-bound and lysosome-related organelle, the melanosome, from MC to KC (Van Den Bossche et al, 2006).…”

The color(s) of human hair—Forensic hair analysis with SpectraCube®

“…Hair color is normally classified through direct comparison with standardized plates [9]. Basically, hair color is determined only by eumelanin and phaeomelanin, whose varying ratios produce the observed color [10]. Apart from the isotopic examination procedures for hair [11] and the toxicological detection methods [12] that are still continuously being improved, the discovery of the so-called genetic fingerprint [13] opened up an entirely new mode of access to hair as material evidence.…”

Influence of different cosmetic vehicles in mechanical and physical properties of hair treated with oxidative hair dyes

“…Hair color produced by melanin vary from brown to black (eumelanin) or yellow to red (pheomelanin). The melanin types determine not only the hair color, but also the chemical composition and physical arrangement of granules in the uniformity related to the distribution of melanin granules into the fiber (Tobin, 2008;Liu et al, 2005). The function of the melanin granules is to effectively absorb light and to protect against damage hair, dark hair containing significantly more melanin than light hair.…”