A Norwegian study suggests that the use of high SPF sunscreen by all women aged 40–75 would reduce melanoma cases by about 18%. An impressive claim to be sure, and the numbers seem to support it, but the findings do make at least one strange claim.
The idea that higher SPF sunscreen could better protect against skin cancer is not revolutionary. Part of the issue is that people don’t reapply or otherwise use sunscreen as recommended. This tends to throw off research and has resulted in conflicting findings in this area of study. Incidentally, there is no indication that how sunscreen was used was accounted for in the study, or even if such a thing was possible.
The study looked at roughly 144,000 women who enrolled in the Norwegian Women and Cancer Study between 1991 and 2007, who were all between ages 40 and 75. Over the 11 year course of the study, there were 772 cases of melanoma. Among the findings of the study:
- Sunscreen users were most likely to report suffering sunburns, going on sunbathing vacations, and using indoor tanning
- Those who used sunscreen with an SPF of 15 or higher at least once in their lives were ~33% less likely to get melanoma than those who only used SPF 14 or lower
- Some predictive number-crunching suggested that if every woman in the 40–75 range used sunscreen with SPF 15+, the rate of melanoma would drop 18%
The findings seem mostly solid, though one particular oddity sticks out: the mention of using SPF 15+ sunscreen at least once made someone 33% less likely to get melanoma. This seems to suggest that a single occasion of SPF 15+ sunscreen at a single point in a person’s life, with weaker sunscreen used every other time, could reduce melanoma risk up to 33%.
It’s a strange finding to make (since melanoma depends on more than one instance of sun exposure) and suggests a situation where the numbers aligned to create a result that is mathematically sound but not found in reality. Or it’s one of those situations where scientific findings can be accurate but simply unintuitive. Or this is just a word choice thing and I am reading way too much into it.
Regardless, the underlying logic and facts of the findings are sound. Using a high SPF sunscreen can help prevent skin cancer and the results are best seen when sunscreen is applied properly and maintained as recommended.
Ghiasvand, R., et. al., “Sunscreen Use and Subsequent Melanoma Risk: A Population-Based Cohort Study,” Journal of Clinical Oncology, 2016; 10.1200/JCO.2016.67.5934.