Does intermittent sun exposure cause basal cell carcinoma? a case‐control study in Western Australia

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Abstract
Our report deals with the relationship of pattern and timing of sun exposure to basal cell carcinoma (BCC) in a population‐based case‐control study conducted in Western Australia in 1988. The main measure of intermittent exposure was based on the amount of exposure on non‐working days relative to that over the whole week. Outdoor recreational activities, holidays and sunburn were also considered to be markers of intermittent exposure. We observed a statistically significant increase in risk of BCC with increasing proportion of weekly sun exposure obtained at the weekend, especially in late teenage (OR = 3.9, 95% CI 1.9‐7.8 for maximum intermittency of exposure), exposure of the site of skin cancer during holidays (OR = 1.9, 95% CI 1.1‐3.1 for the highest exposure quarter) and sunburn to the site (ORs of 1.8 for 3‐10 and 1.5 for 11+ sunburns in a lifetime). Risk of BCC increased substantially with increasing intermittency in poor tanners but not at all in good tanners. Our data suggest that a particular amount of sun exposure delivered in infrequent, probably intense increments will increase risk of BCC more than a similar dose delivered more continuously over the same total period of time.