Pigmentary changes of the ageing skin.

In subjects older than 25-30 years the number of enzymatically active melanocytes detectable by the dopa reaction decreases by about 10-20% per decade, with exposed skin having approximately twice as many pigment cells as unexposed skin. Chronic exposure to sunlight may stimulate the epidermal melanocyte system rather than accelerating chronological ageing. The number of melanocytic naevi declines with age. Despite the decreased melanocyte density, photoaged skin has irregular pigmentation and, frequently, there is hyperpigmentation. This may be due to greater positivity of dopa of chronically irradiated melanocytes. Heterogeneity in skin colour in exposed areas of skin is due to uneven distribution of pigment cells, a local loss of melanocytes, and a modification in the interactions between melanocytes and keratinocytes. The most common pigmented lesions in sun-exposed skin include ephelides, actinic lentigo, pigmented solar keratoses and seborrhoeic keratoses, and lentigo maligna. The white spots in aged skin are usually stellate pseudoscars or idiopathic guttate hypomelanosis. Greying of the hair is due to progressive loss of melanocytes from the hair follicles. In vivo and in vitro studies are necessary to increase overall understanding of the processes involved and to improve treatment of the pigmentary changes in ageing skin.