Ultrastructural characterization of the distribution of melanin and epidermal macrophages in photodamaged skin.

We examined the characteristics of melanin distribution, the possible mechanisms underlying the histological incontinence of pigment, and the significance of epidermal macrophages in photodamaged skin. We used electron microscopy to compare and quantitate melanin distribution in various types of cells and structures, to qualitatively observe associations of melanin granules with melanophages, and to examine morphological differences of epidermal macrophages in sun-exposed versus sun-protected facial skin. Melanin-containing cells (such as Langerhans' cells) and melanin-containing structures (such as colloid bodies) in photodamaged skin were more numerous than in sun-protected skin, in proportion to differences in melanocyte density and in epidermal melanin content. Although the precise mechanism(s) of histological incontinence of pigment in photoaging skin appear to be very complicated, it is certainly one of the morphological hallmarks of photodamaged facial skin, and the degeneration of keratinocytes (noted by their electron-lucent properties), a feature characteristic of photoaging, contributes to that process. Furthermore, the increased numbers of epidermal macrophages in sun-exposed skin may be associated with photoaging processes (probably through their phagocytic function) as well as alterations of the cutaneous immune system.