The risk factors for developing keratinocyte cancer include the following.

Environmental and exogenous risk factors:

• chronic sun exposure
• multiple solar keratoses
• solarium use
• intensive UV exposure in childhood and adolescence – this is a stronger causative factor for developing BCC, whereas SCC is associated with chronic sun exposure over decades (Leiter & Garbe 2008); sun exposure in adulthood, however, is an important risk factor for both SCC and BCC (Iannacone et al. 2012).
• past exposure to arsenic.

Personal risk factors:

• some rare genetic conditions predisposing to skin cancer
• skin types I and II (these have a higher risk of sunburn)
• a history of blistering sunburn
• increasing age
• a previous diagnosis of melanoma or BCC/SCC (up to 60 per cent grow another within three years)
• solar keratoses.

Lifestyle risk factors:

• outdoor occupations
• recreational sun exposure.

Medical risk factors

• UVA and psoralen (PUVA) treatment for psoriasis
• immunosuppression (e.g. post transplantation, chronic lymphomas and leukaemias)
• previous radiotherapy
• some photosensitising medications (e.g. methotrexate and voriconazole).