Oral administration of green tea or caffeine to hairless SKH-1 mice for 2 weeks stimulated UV-induced increases in apoptotic sunburn cells in the epidermis, and a similar effect was observed when caffeine was applied topically immediately after UV. In mice pretreated with UV for 22 weeks (high-risk mice without tumors), topical applications of caffeine 5 days a week for 18 weeks with no further UV treatment inhibited carcinogenesis and stimulated apoptosis in the tumors. Oral administration of green or black tea to UV-pretreated high-risk mice for 23 weeks inhibited skin tumorigenesis, decreased the size of the parametrial fat pads and decreased the thickness of the dermal fat layer away from tumors and directly under tumors. Administration of the decaffeinated teas had little or no effect on these parameters and adding caffeine to the decaffeinated teas restored their inhibitory effects. Administration of caffeine alone also inhibited carcinogenesis and decreased the size of the parametrial fat pads and the thickness of the dermal fat layer. Using data from individual mice and linear regression analysis, we found a highly significant positive correlation between the thickness of the dermal fat layer away from tumors and the number of tumors per mouse.