Residential ambient ultraviolet B and ultraviolet A and incidence of keratinocyte carcinoma in the nationwide US Radiologic Technologists cohort.

Background: Few epidemiological studies have distinguished the effects of solar ultraviolet radiation (UVR) wavelength, including UVB and UVA, on the risk of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin.

Objective: We aimed to evaluate the association between ambient UVB and UVA with BCC and SCC incidence.

Methods: Using data from the nationwide U.S. Radiologic Technologists cohort, satellite-based noontime ambient UVR was obtained based on residential history (<13, 13-19, 20-39, 40-64, and ≥65 years). Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were estimated for associations between UVB, UVA quintile (Q), and first primary BCC and SCC in mutually adjusted and stratified models, additionally adjusted for sun sensitivity characteristics.

Results: There were 62,595 non-Hispanic White participants aged 22-90 years at baseline (1983-1998). During a median 25.5 years of follow-up, 6,339 incident BCCs and 1,253 incident SCCs were reported. Annual and summer UVB and UVA were each positively associated with both BCC and SCC risk before mutual adjustment. After adjusting for UVA, summer (but not annual) UVB Q5 versus Q1 was associated with BCC (IRR=1.41; 95% CI: 1.13, 1.77) and SCC (IRR=1.69; 95% CI: 1.01, 2.84). After adjusting for UVB, annual (but not summer) UVA Q5 versus Q1 was associated with BCC (IRR=1.42; 95% CI: 1.13, 1.77) and SCC (IRR=1.84; 95% CI: 1.10, 3.06).

Conclusions: Both summer UVB and annual UVA were independently associated with both higher risks of BCC and SCC. Our results suggest that cumulative lifetime UVA may be an underappreciated contributor to BCC and SCC risk. With confirmation, these findings suggest public health interventions promoting avoidance of excessive UVB and UVA among susceptible populations.