Basal Cell Carcinoma
Different patterns of sun exposure appear to lead to different types of skin cancer among susceptible individuals. Intermittent sun exposure seems to be the most important risk factor for melanoma. BCC appears to share some risk factors with melanoma.[2,3] Some BCCs may be caused by chronic sun exposure, but a large portion (one-third or more) is apparently caused by intermittent sun exposure, similar to that implicated in melanoma. Occupational exposures are associated with SCC risk and recreational exposures with BCC risk. This exposure-response pattern is consistent with the results from a randomized trial of sunscreen efficacy that found statistically significant protection for the development of SCC but no evidence at all for protection from the development of BCC.
Other environmental factors
Environmental factors other than sun exposure may also contribute to the formation of BCC and SCC. Petroleum byproducts (e.g., asphalt, tar, soot, paraffin, and pitch), organophosphate compounds, and arsenic are all occupational exposures associated with cutaneous nonmelanoma cancers.[5,6,7]
Arsenic exposure may occur through contact with contaminated food, water, or air. While arsenic is ubiquitous in the environment, its ambient concentration in both food and water may be increased near smelting, mining, or coal-burning establishments. Arsenic levels in the U.S. municipal water supply are tightly regulated; however, control is lacking for potable water obtained through private wells. As it percolates through rock formations with naturally occurring arsenic, well water may acquire hazardous concentrations of this material. In many parts of the world, wells providing drinking water are contaminated by high levels of arsenic in the ground water. The populations in Bangladesh, Taiwan, and many other locations have high levels of skin cancer associated with elevated levels of arsenic in the drinking water.[8,9,10,11,12] Medicinal arsenical solutions (e.g., Fowler's solution and Bell's asthma medication) were once used to treat common chronic conditions such as psoriasis, syphilis, and asthma, resulting in associated late-onset cutaneous malignancies.[13,14] Current potential iatrogenic sources of arsenic exposure include poorly regulated Chinese traditional/herbal medications and intravenous arsenic trioxide utilized to induce remission in acute promyelocytic leukemia.[15,16]