The answer varies: For SCCs, very effective; for BCCs, not so much.
Dermatologists routinely recommend sunscreen for protection against nonmelanoma skin cancers, but little evidence supports this recommendation. In one of the few studies to address this important issue (see Lancet 1999; 354:723 and 1038), researchers found that daily sunscreen use over a 4.5-year period produced a 35% reduction in the incidence of squamous cell carcinomas (SCCs) but had no effect on the incidence of basal cell carcinomas (BCCs). The researchers continued to follow the participants after the study ended to determine whether the treatment regimen would have a lasting effect on SCCs and whether there might be a late effect on BCC occurrence.
In the original study, 1621 subjects from Queensland, Australia, were randomized to one of two groups: The intervention group was instructed to apply SPF 16 sunscreen on a daily basis, and controls were told to continue their usual sunscreen usage, including non-use. When the study ended, no specific recommendations were given regarding further sunscreen use, and volunteers were followed for another 8 years. After the extended follow-up, those who had been in the daily-sunscreen group continued to have a 35% to 38% reduction in SCC incidence compared with controls, but there was still no statistically significant difference in BCC incidence between groups. The authors attribute most of the prolonged effectiveness to the original period of daily sunscreen use, but they also note that the intervention group continued to use sunscreen more frequently than the control group in the follow-up period (25% vs. 18%; P=0.004).
Comment: Why sunscreen is less effective for BCCs than for SCCs is unclear. All the participants in this study were adults; we do not yet know the effects on BCC incidence of early and sustained sunscreen prevention in children, teenagers, and young adults. These results highlight the need for chemopreventive agents in addition to sunscreen for nonmelanoma skin cancer prevention.
— Craig A. Elmets, MD
Published in Journal Watch Dermatology January 12, 2007