1. EXPOSURE TO CARCINOGENIC FACTORS
- Ultraviolet light - Basal cell cancers are more related to intermittent sun exposure and sunburns, especially in childhood and adolescence.
- Ionizing radiation such as radiotherapy may also increase of skin cancers.
- Chemicals such as arsenic increase the risk of skin cancers. Exposure is usually chronic and at low concentrations.
2. GENETIC SYNDROMES
There are a number of genetic syndromes which increase the risk of skin cancers. These include xeroderma pigmentosa which is a defect in DNA repair. This condition is associated with sun sensitivity, extensive freckling and the risk of non-melanoma skin cancers is almost 5,000 times that of the normal population.
Basal cell carcinomas are increased in the nevoid basal cell carcinoma syndrome as well as Gorlin's syndrome.
Chronic non-healing wounds such as chronic ulcers and thermal burns and other non-healing wounds have an increased risk of basal cell carcinomas.
Individuals who are immunosuppressed such as after kidney or heart transplants have a tenfold risk of basal cell cancer.