Too much sunlight can cause sunburn, and sunburn is a risk factor for skin cancer. So, if sunscreens help prevent sunburn, they should reduce the risk of skin cancer too, right? It turns out, according to a piece appearing last month in the journal Clinical Pharmacology and Therapeutics, that the evidence that sunscreens protect against skin cancer turns out to be a bit thin on the ground [1].
Skin cancers come in three main forms: the quite-often deadly malignant melanoma, as well as squamus cell carcinoma and basal cell carcinoma that are not nearly as life-threatening. The author of the Clinical Pharmacology and Therapeutics piece cites a randomised study in which individuals used daily sunscreen or no daily sunscreen for 4.5 years. The study looked only at squamous cell and basal cell carcinomas. The result was that the development of new cancers was essentially the same in both groups. In other words, the application of sunscreen did not appear to protect against the development of new skin cancers.
Turning out attention for a moment to malignant melanoma, the article states: “Unfortunately, no melanoma study has shown convincingly that sunscreen use reduces the risk of melanoma.” The piece goes on to speculate why this might be. A few theories are put forward, which include:
- The sorts of people who use sunscreen (e.g. fair-skinned) are generally at enhanced risk of skin cancer to begin with.
- Sunscreens often protect against burning by blocking ultraviolet B (UVB) rays, but may allow longer exposure to potentially damaging rays from other parts of the spectrum such as UVA.
- Many people who use sunscreens do not apply them properly.
- Sunscreen may block the manufacture of vitamin D (which is linked to cancer-protective effects). This mechanism is viewed as of doubtful significance by the author, who refers to the fact this is only likely to an issue in those who apply the sunscreen properly.
- The potentially carcinogenic effect of certain chemicals used in sunscreens including avobenzone (Parsol 1789) and ecamsule (Mexoryl SX).
The article goes on to refer to the fact that “…interests that are not scientifically based seem to be driving the heavy reliance on sunscreens as the first line of prevention against skin cancer,” adding “The fervor with which companies promote sunscreen can perhaps be traced to the profit that sunscreen sales bring.”
The piece also states: “Death from skin cancer is advertised as being avoidable with the use of sunscreens. This position might actually be true, but there is as yet absolutely no scientific evidence to support it.”
For more information on safe sun exposure including the use of clothing and shade, see here.
References:
1. Berwick M. The good, the bad and the ugly of sunscreens. Clinical Pharmacology and Therapeutics 2011;89(1):31-33
