Behavior of Hair Follicles in Vitiligo: Clinical Presentation and Discussion

The “follicular-melanin unit” is residing in the “immune privileged” proximal hair bulb [3]. This follicular-melanin unit consists of one melanocyte for every five keratinocytes in the hair bulb as a whole; the ratio is 1:1 in the basal epithelial layer next to the dermal papilla [4]. Hair bulb melanogenic melanocytes differ from epidermal melanocytes in being larger, with longer and more extensive dendrites, producing twoto four fold larger melanosomes (Figure 1). Melanocytes of the hair bulb are known to have potential proliferation power and are not as indolent as epidermal melanocyte lacking completely this power of renewal. The hair bulb melanocyte system has been perceived as selfperpetuating whereby melanocytes involved in the pigmentation of one generation are also involved in the pigmentation of the next wave [5,6]. Follicular melanogenesis is characteristically cyclic in nature, as opposed to the continuous melanogenesis of epidermal pigmentation [7].