Specific patterns of sun exposure appear to lead to different types of skin cancer among susceptible individuals. Intense intermittent recreational sun exposure has been associated with melanoma and BCC,[2,3] while chronic occupational sun exposure has been associated with SCC. Given these data, dermatologists routinely counsel patients to protect their skin from the sun by avoiding mid-day sun exposure, seeking shade, and wearing sun-protective clothing, although evidence-based data for these practices are lacking. The data regarding skin cancer risk reduction by regular sunscreen use are variable. One randomized trial of sunscreen efficacy demonstrated statistically significant protection for the development of SCC but no protection for BCC, while another randomized study demonstrated a trend for reduction in multiple occurrences of BCC among sunscreen users  but no significant reduction in BCC or SCC incidence.
Level of evidence (sun-protective clothing, avoidance of sun exposure): 4aii
Level of evidence (sunscreen): 1aii
Tanning bed use has also been associated with an increased risk of BCC. A study of 376 individuals with BCC and 390 control subjects found a 69% increased risk of BCC in individuals who had ever used indoor tanning. The risk of BCC was more pronounced in females and individuals with higher use of indoor tanning.
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.[9,10,11]
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.[12,13,14,15,16] 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.[17,18] 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.[19,20]