Effect of long-term exposure to su-light on the ultrastructure of epidermal melanin unit of the human skin

ABSTRACT

The aim of the present work was to study the ultrastructural features of the melanocytes and related keratinocytes in chronically sun- exposed skin. 10 fair-skinned adult males, whose occupation required long exposure to sun light were chosen for this study. Chronic exposure to sun light enhanced the proliferative activity of the epidermal melanocytes accompanied by increased melanin content, variable dendritic morphology and appearance of numerous pinocytotic vesicles and vacuoles. Moreover, migration of melanocytes were demonstrated in the sun-exposed skin into suprabasal and subbasal [dermal] positions. Groups of melanocytes were demonstrated in the superficial part of the dermis denoting nest formation. In addition, chronic exposure to sun light induced marked proliferation of the epidermal keratinocytes leading to increased epidermal thickness. Also, their pigment content was increased due to enhanced melanin transfer from the nearby melanocytes. Moreover, there was concentric condensation of the excess melanin pigments and cytoplasmic tonofilaments around their nuclei forming a shield to protect the nuclear DNA against the harmful effect of solar ultraviolet rays