The carcinogenicity (photocarcinogenicity) of sunlight to human skin has been recognized more than a century ago. Last decades numerous experimental studies show that UV rays damage DNA, cause gene mutations leading to the development of malignant tumors such basal cell carcinomas, squamous cell carcinomas and melanomas. The tumors occur most frequently in fair skinned people, and the mutations typically are found at dipyrimidine sites with C-T or / and CC-TT tandem double mutations. The authors briefly summarize their investigation of the p53 suppressor gene, and expose their hypothesis of hTERT involvement in cancerogenesis. Also their underline the importance of UV induced immunosuppression in photocarcinogenesis. Psoriatic patients are exposed to numerous cancerogens in their treatment. A better understanding of the mechanisms of photocarcinogenesis could provide new ways in the treatment of skin tumors.