The senile epidermis: environmental influences on skin ageing and cutaneous carcinogenesis

There is a wealth of new knowledge regarding mechanisms of carcinogenesis and their interaction with senescence and environmental insults, particularly on the effects of UV irradiation on the skin. Innovations and advances in tissue culture techniques now permit in vitro studies of keratinocytes and other benign and malignant skin-derived cells. The ageing processes and cutaneous neoplasia, therefore, can now be studied at the cellular level. New insights regarding the interrelationship of ageing, environment and cutaneous neoplasia are close at hand. Depletion in the number of Langerhans cells and suppression of their function in ageing and UV-exposed skin may allow tumour cells to overcome the host's defence system. The potential increase in UV irradiation due to depletion of the ozone layer may increase the incidence of skin tumours. Carcinogenesis involves three distinct steps: initiation, promotion, and malignant conversion. The mechanism has been studied in mice, where it is suggested the c-ras oncogene may play an important role.