The exposure of mammalian cells to ultraviolet radiation (UV) leads to DNA damage, resulting in mutation and possible cancer. UV irradiation has been shown to act both as a tumor initiator and as a tumor promoter. The initiation step by UV involves genetic changes in oncogenes and tumor suppressor genes such as ras, p53, and patched. p53 mutations can be detected in normal skin from sun-exposed sites, indicating the early event of multi-step carcinogenesis. Furthermore, the activation of telomerase may precede the p53 mutation. The molecular mechanisms of UV-induced tumor promotion, principally the epigenetic phenomenon, remain elusive. Molecules acting as tumor promoters in photocarcinogenes include PKC, free radicals, tumor necrosis factor-α, and cyclooxygenase-2. In addition, UV-induced apoptosis is deeply involved in tumor promotion, because resistance to apoptosis is closely associated with the acceleration of tumor formation. The roles of p 53, Fas/FasL, tumor necrosis factor-α, nerve growth factor, and DNA damage in UV-induced apoptosis are discussed.
Chemical peeling is a dermatological treatment for certain cutaneous diseases or conditions or aesthetic improvement; it consists of the application of one or more chemical exfoliating agents to the skin. Recently, in Japan, chemical peeling has become very popular for medical as well as aesthetic treatment. Because the scientific background and an adequate approach are not completely understood or established, medical and social problems have been reported. This prompted us to establish and distribute standard guidelines for chemical peeling. These guidelines include the minimums for the indications, the chemicals used, their applications, associated precautions, and postpeeling care and findings. The principles are as follows. 1) Chemical peeling should be performed under the control and the responsibility of a physician. 2) The physician should have knowledge of the skin and subcutaneous tissue and understand the mechanism of wound-healing. 3) The physician should be board-certified in an appropriate speciality such as dermatology. 4) The ultimate judgement regarding the appropriateness of any specific chemical peeling procedure must be made by the physician in light of all the standard therapeutic modalities which are appropriate for the individual patient.