There was a recent article in the NEJM about regulation and sunscreens. Much of this world is more regulation than science, a la the murky worlds of pharma, and more about shifting units than providing value. I wrote a letter highlighting some of the problems of confusing ‘regulation’ with ‘science’. The text is below. Links here and here.
The role of UVA, and sunscreens in preventing skin cancer
The statement that UVA is ‘most closely linked to cancer’ is lacking in nuance. The evidence is probably firmer for UVB for some types of skin cancer, but there remains genuine debate about UVA, especially for melanoma. The attempt to demarcate sunscreens that prevent burning from those that might prevent cancer, is misplaced. Damage from UVR is a continuous variable,and burning is not a well defined term operationally. Erythema varies across orders of magnitude of UVR exposure,and it is easy to demonstrate DNA damage without erythema. If you prevent ‘erythema’ or ‘sub-erythema’ (that is changes in blood flow that you can measure but not see) you might imagine that you will prevent cancer in the long term, although the evidence to support this reasonable belief is sparse, especially for melanoma. Pretending that only a sunscreen with a SPF greater than 15 can achieve this, whereas those beneath 15 ‘just’ reduce erythema, seems to me to be taking a liberty with scientific common sense. How the sunscreens are used in the real world (thickness, frequency of re-application) probably adds in more variance, as the author notes.