With summer on its way, we all get excited about the sun and the warmth, even us poor souls living in Scotland, where our chances of getting either are depressingly low. We do get, though, a huge number of articles about skin cancer and sunscreen. On the 15th of May the consumer agency Which? published that some commercialized sunscreens do not protect the skin as much as they claim. While their methods are not transparent and they publish their conclusions rather than their results, this report is certainly worrying. This news was echoed by “The Guardian” and “BBC” amongst others. The “Daily Record” went one step further (in yet another example of awfully communicated science) and reported that “Your sunscreen may not really be saving you from cancer” and that “it could in fact be causing problems rather than stopping them”. “The Scotsman” further claimed that there is an “Increase in rickets linked to overuse of sunscreen”. While fraudulent claims about sun protection should certainly be reported, it should be kept in mind that using sunscreen is one of the only effective measures to protect us from skin cancer.
Exposure to the sun is related to 65-90% of all cases of melanoma, the most dangerous type of skin cancer. The outer layers of our skin can’t stop ultraviolet radiations of the sun (UV) from getting in contact with the more vulnerable inner layers, potentially damaging the structure of our DNA and causing mutations which can lead to cancer. Sunscreen contains substances able to protect our skin by filtering the UV rays. Their efficiency is generally rated by the Sun Protection Factor (SPF) system, which measures how long the skin will be protected from UVB (at the time when SPF was invented, it was thought that only the UVB rays were dangerous for the skin, and not UVA or UVC). For example, an SPF of 20 should mean that the protected skin would take 20 times longer than the unprotected skin to get burnt under the same amount of radiation. Sunscreens are now incorporating protection against UVA rays as well, which is in general rated with stars or labelled “broad spectrum”.
Broad spectrum sunscreen does protect from melanoma, as clearly shown by a study on animal models published in Nature in 2014. However, the same study showed that no matter the SPF the skin ends up getting burnt and damaged. And that brings us back to the title of the Daily record article, “Your sunscreen may not really be saving you from cancer”, when it should say “Your broad spectrum sunscreen will protect you from cancer if you´re sensible with your sunbathing and use sunscreen abundantly and frequently”, which admittedly is a far less catchy headline.
What about the claim that sunscreen might cause problems by preventing the production of vitamin D? Vitamin D is necessary for the absorption of calcium, and its deficit results in a severe disease of the bones called ostemalacia (rickets when it happens in children). Vitamins are by definition substances that the body needs, usually in very small quantities, but can´t produce by itself, so they have to be provided generally with food. The problem with Vitamin D is that it is scarce in food, and only 20% of our Vitamin D is provided through the diet. Most of it is built in the body using cholesterol which needs to be exposed to UVB rays to become Vitamin D.
So does sunscreen allow enough production of vitamin D? So far no studies have found an association between use of sunscreen and health-threatening levels of vitamin D. “The Scotsman” bases its article on the work of a professor who has published a study reporting an increase in incidence of deficit of vitamin D in kids in the UK, but not the role of sunscreen, so no story there. Amongst the studies which do investigate the possible link between sunscreen and lower levels of Vitamin D, only some do observe a sunscreen-related decrease, and only in individuals under very strict sun protection. Of note, most of them have a terrible experimental approach, but I don’t have time to comment on that. Anyway, none of them reports health problem derived from this decrease.
So, in conclusion, be sensible, use sunscreen and enjoy your summer.