Epidemiological aspects of photocarcinogenesis

Abstract

Epidemiologically, it is hard to distinct the effects of component radiations because sunlight is considered as a whole entity. Human skin may experience either acute (immediate reaction) or chronic (repeated) sunlight exposure. UV radiation coming through sunlight is absorbed by human skin and causes various degrees of damage. However, melanin pigment in the skin acts as a natural sunscreen and absorbs and prevents from detrimental consequences of UV radiation. Repeated and extended UV exposure causes development of photoaging, i.e., premature skin aging and photocarcinogenesis. Photo-induced cancers particularly include malignant melanomas and carcinomas, i.e., basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). High-UV radiation environment leads to evolution of permanently dark constitutive pigmentation which is resistant to UV radiation. However, light-skinned people experience premature skin aging on repeated exposure. Therefore, prevalence of photocarcinogenesis is highest in lightly pigmented people (Halder and Bridgeman-Shah: Cancer 75(S2):667-673, 1995). Development of photocarcinogenesis is dependent on various factors including ethnic origin, place of residence, anatomic site exposed, outdoor and indoor activities, total exposure duration, time of exposure, and ambient sunlight intensity. Photocarcinogenesis is predominantly a disease of people of European origin. Its rate is very low in Asia and in the United States. It is more frequently observed in white-skinned than dark-skinned people.