A 68-year-old Caucasian man of Norwegian extraction presents to the dermatology clinic for evaluation of a new growth on the right nasal wall. He states that it has been present for approximately 6 months, has grown, is tender to the touch & occasionally bleeds with minimal trauma. On examination, there is a pearly papule with a slightly rolled border & branching telangiectasias throughout the lesion. Patient inquires about the risk factors associated with his skin lesion. You inform him that the most important risk factor is