You’d be surprised. There’s a difference between preventing sunburn and preventing other types of skin damage. Some sunscreens can do both, but others can’t.
Sun damage, as you may have heard, is caused by exposure to ultraviolet rays, or UV rays. Sunscreen manufacturers generally talk about two different kinds of UV — UVA and UVB — and both of them are implicated as causes of skin cancer. But don’t be fooled. The ubiquitous labels about SPF, or sun protection factor, really just refer to a sunscreen’s ability to protect against burning, which it turns out is mostly caused by UVB. (You can find out more about all this from the American Academy of Dermatology.) Doctors’ groups now recommend you buy a broad-spectrum sunscreen that specifically states it will protect against both UVA and UVB radiation.
I strolled over to my local drugstore earlier this afternoon to see how the products fared. Almost all of them did offer UVA and UVB protection. But not all of them. Turns out we still need to read the labels.
In recent years you may have also heard a rumor that sunscreen can in fact cause skin cancer. Most of these rumors appear to be either myths or mistakes, with only the flimsiest of evidence behind them. But there is one especially compelling argument on this front: it seems that wearing sunscreen — and avoiding sunburn — encourages users to stay in the sun for longer than they should. A study in the British Journal of Cancer in 2000 found that holiday-goers who were given SPF-30 sunscreen spent more time in the sun and actually had greater daily UVB exposure than holiday-goers who were just given SPF-10 sunscreen. People were lulled into a false sense of security because they hadn’t burned. Remember, no sunscreen blocks all rays. So even when you’re not feeling the sun’s effects, you’re still experiencing some of them.