Abstract
The color of the hair is dependent on the existence and function of the melanin producing cells, the melanocytes, in the hair matrix of the bulb. In vitiligo, the loss of color of the affected skin is due to loss of epidermal melanocytes, which may also be accompanied by loss of the bulbar melanocytes with subsequent loss of the hair color. Lymphocytic immune-cytotoxic process maybe involved in the destruction of epidermal or bulbar melanocytes. Hair depigmentation is said to follow surface depigmentation in long standing disease. This delay in development of leukotrichia in vitiligo could be claimed to the difference in melanization nature of hair follicle in comparison to epidermal melanization process. In rare cases, follicular melanocytes can be primarily destroyed in vitiligo without destruction of epidermal melanocytes. Apart from mature melanocytes, the hair follicles possess also immature form of melanocytes residing in the bulge area, outer root sheath, dermal papilla and sometimes the hair matrix. These immature cells usually escape the vitiligo immune destructive process. The existence of leukotrichia used to be a sign of disease recalcitrance and expected treatment failure. In such cases several surgical procedures were introduced to help repigmenting the skin. It was found that activation of the immature melanocytic precursors in hair follicles is responsible for the repigmentation of epidermis and hair follicles due to the supply with new mature melanocytes.
Highlights
The color of the hair is dependent on the existence and function of the melanin producing cells, the melanocytes, in the hair matrix of the bulb
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 follicles in vitiligo my retain their normal color or lose it independently from disease duration, severity or extension
Summary
The hair bulb is the only site of pigment production for the hair shaft and contains highly melanogenic melanocytes and a minor subpopulation of poorly differentiated pigment cells [1]. In the adult hair follicle, pigmentation results from interactions between follicular melanocytes, matrix keratinocytes, and Dermal Papilla (DP) fibroblasts [2]. 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]. Oxidative stress can affect follicular melanocytes over time and may be a major factor in the loss of hair pigment, the reduction in overall numbers of melanocytes per follicle, and for induction of white hairs [9]
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