Age Incidences of basal cell carcinoma, squamous cell carcinoma and melanoma all increase dramatically with age. UV exposure Skin cancer incidence is highest in areas with the most ambient sunlight exposure (equatorial, high altitude). Occupational or recreational UV exposure. History of blistering sunburns seems particularly relevant to melanoma, whereas cumulative/chronic UV dose may be more predictive of keratinocyte malignancies.  Tanning bed use clearly is associated with BCC, SCC and melanoma.  First exposure to indoor tanning before 35 years of age raises lifetime risk of melanoma by 75% Fair skin complexion Fair skin complexion, caused by scant deposition of the highly UV-protective eumelanin pigment in the epidermis, is associated with higher risk of BCC, SCC and melanoma. In fair skin, more UV penetrates into the skin and promotes mutagenesis and carcinogenesis.  Albinos, who lack pigment entirely due to loss of function of melanogenic biosynthetic enzymes, are at particularly high risk for skin cancer (particularly BCC and SCC).  Cancer risk is also associated with an inability to tan adaptively. Personal or family history of skin cancer Once a person has been diagnosed with skin cancer, their risk for others is heightened. Up to 10% of melanoma patients will develop a second melanoma in their lifetime. Inherited CDKN2A defects (the gene that encodes the p16INK4A and p14ARF tumor suppressors) is associated with familial melanoma Moles (nevi) Many melanomas appear to arise from pre-existing moles.  Benign nevi and melanoma both frequently exhibit gain-of-function mutation in the B-Raf gene. Immune suppression Immunosuppressive therapies (e.g. for treatment of autoimmune disorders, GVHD or rejection of solid organs in transplant recipients, heightens risk for melanoma, BCC and SCC. Chemotherapy also increases risk for skin cancers. Ionizing radiation Particularly for SCC.  DNA repair deficiency Xeroderma pigmentosum (XP) patients who lack one of at least eight enzymes in a common  nucleotide excision repair (NER) pathway have a 2,000-fold increased risk of skin cancers, including melanoma.  Latency is much shorter in XP patients that in the general population, with many skin cancers developing in childhood on UV-exposed skin. Heavy metals Chromium, cobalt and other metals may promote free radical formation through Fenton chemistry, contributing to oxidative mutagenesis and carcinogenesis

Table 1: Major risk factors for skin cancers.