Melanin and melanocytes. Many different assumptions have been made with respect to the causes of vitiligo: according to some researchers, vitiligo is the result of certain active or past diseases; others claim it is due to genetic susceptibility. For some authors, the disease is triggered by stress conditions or on-going physical traumas or micro-traumas; for others by stress or physical traumas. Fig. 3 summarizes the data found in this respect in cases treated from 1990 to 1995 by the Ratok®derm Medical Dermatological Centre of Milan for the focused punctiform treatment of vitiligo by means of an advanced technology. Multiple factors are certainly involved in the etiopathology of vitiligo; a special medical branch, known as psycho-neuro-immunology, devotes to the study of interactions between the psyche, the nervous system, the immune system, and the skin. Vitiligo could belong to a group of skin diseases caused by an impaired balance of these sensitive elements, which are known to be strictly dependent on each other. However, while the causes of vitiligo are still mostly unknown, one thing is known for certain, namely that a microscopic examination of a skin fragment taken from an achromic region reveals that melanocytes are absent, and so is melanin, the pigment responsible for the colour of the skin, of the hair, of the chorioid, and of some mucosal tissues. (At the Ratok®derm Medical Dermatological Centre of Milan, the absence of melanin is ascertained noninvasively by means of the videodermatoscopic investigation shown in  Fig. 4). Melanin is processed by melanocytes, cell elements disseminated in the innermost skin layer, the basal layer  (Fig 5). Melanocytes are photoreceptors, i.e. cells allowing the skin to absorb the light energy required to trigger the processes promoting melanin production (Fig. 6). Melanocytes then play a crucial role both in the onset and in the subsidence of vitiligo. For still virtually unknown reasons, melanocytes may indeed be reduced in number, replaced by other cells, or prevented from producing melanin: in this case the cells moving up from the skin basal layer to higher skin layers will be devoid of melanin  (Fig. 7) once they reach the surface, they will give place to an achromic patch  (Fig. 8) which may be repigmented by means of a treatment capable of restoring or reactivating melanocytes (Fig. 9).