1)                        Actinic Keratosis (AK) [4, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

2)                        Albinism [20]

3)                        Arsenic exposure [21]

4)                        Burn scars/chronic inflammation [8, 22, 23, 24]

5)                        Chemical/occupational exposures [25, 26]

6)                        Cigarette smoking [27]

7)                        Ethnicity [10, 28, 29, 30, 31, 32]

8)                        Familial predisposition [33, 34]

9)                        Human Immunodeficiency Virus [35]

10)                   Human Papillomavirus [36, 37]

11)                   Lymphoproliferative disorders [4, 38, 39]

12)                   Organ transplantation/chronic immunosuppression [40, 41, 42, 43, 44, 45]

13)                   Prior skin cancers [46]

14)                   Radiation exposure [25, 40, 47, 48]

15)                   Selenium supplementation [49]

16)                   Sun (UVA/UVB) exposure [4, 22, 29, 50, 51, 52]

17)                   Xeroderma Pigmentosum [53]