Biology of hair follicle pigmentation

Abstract

• The hair follicle and epidermal pigmentary units are broadly distinct and can be distinguished principally on the basis of the former's stringent coupling to the hair growth cycle compared to the latter's continuous melanogenesis. • Melanin synthesis and its transfer from melanocyte to hair bulb keratinocytes both depend on the availability of melanin precursors and are regulated by cutaneous signal transduction pathways that: (1) are both dependent and independent of receptors, (2) act through auto-, para-or intracrine mechanisms, and (3) can be modified by hormonal signals. • Follicular melanocytes appear to be more sensitive than epidermal melanocytes to aging influences, as indicated by dramatic hair graying/canities. This is likely to reflect differences in the epidermal and follicular microenvironments. • Skin and hair color contribute significantly to our overall visual appearance and to social/sexual communication; thus disorders of follicular pigmentation may cause psychological trauma. • Hair pigment may also contribute to rapid excretion of heavy metals, chemicals, and toxins from the body by their selective binding to melanin. • The availability of cell culture methodology for isolated hair follicle melanocytes and for intact anagen hair follicle organ culture, as well as improved technologies for follicular delivery in vivo should provide important research tools for elucidating the regulatory mechanisms of hair follicle pigmentation. © 2008 Springer-Verlag.