It does successfully prevent sunburn, but what about the evidence for sunscreen protecting you from skin cancer later in life?
The answer: Nobody is really sure. Last year, I wrote a short piece for BoingBoing that looked at this a little bit. The key point: Cancer takes a long time to happen and we haven't been using sunscreen long enough to have much evidence about it.
But, at Discover's The Crux blog, Emily Elert expands on some of the other problems in play. One of the key things—and something that will hopefully be fixed by this time next year—there's nothing on the sunblock you buy to tell you how protective it is against skin cancer. SPF is all about the burn. So even if some sunscreens do protect against cancer, you don't have a good way to know whether or not you're using one of them.
Read the rest
First of all, the way sunscreen’s effectiveness is measured—its SPF rating—basically only describes its ability to block UVB rays. That’s because UVB is the main cause of sunburn, and a sunscreen’s SPF stands for how long you can stay in the sun without getting a sunburn (a lotion that allows you to spend 40 minutes in the sun rather than the usual 20 before burning, for example, has an SPF of 2).
UVA rays can cause cancer but not sunburn, so they don’t factor into the SPF calculation. That means that if you slather on a high SPF sunscreen that only protects against UVB, you’d still absorb lots of UVA radiation, potentially increasing your long-term cancer risk.
A few days ago, I saw this photo on a friend's Facebook feed, accompanied by a caption claiming that it showed a truck driver who had exposed half his face to the sun for 30 years.
There wasn't any link and naturally, being Facebook, I assumed this was probably not an accurate description of what was going on in the photo and kind of just brushed it aside.
And then Mo Costandi posted the same photo on Twitter along with a link to its original source—The New England Journal of Medicine. Oh, s&*%.
The patient reported that he had driven a delivery truck for 28 years. Ultraviolet A (UVA) rays transmit through window glass, penetrating the epidermis and upper layers of dermis. Chronic UVA exposure can result in thickening of the epidermis and stratum corneum, as well as destruction of elastic fibers. This photoaging effect of UVA is contrasted with photocarcinogenesis. Although exposure to ultraviolet B (UVB) rays is linked to a higher rate of photocarcinogenesis, UVA has also been shown to induce substantial DNA mutations and direct toxicity, leading to the formation of skin cancer. The use of sun protection and topical retinoids and periodic monitoring for skin cancer were recommended for the patient.
Basically, this gentleman does not yet seem to have skin cancer. Instead, the skin on that side of his face had thickened (a sign that his skin cells aren't growing and sloughing off in a normal way). The elastic tissue on that side of the face had also started to degenerate, leaving deep wrinkles, as well as wide pores that became multiple blackheads. Read the rest