This may come as a shock to some of you (it certainly was to me), but not all sunscreen in the US is made to protect you from skin cancer. High SPF numbers aren’t the only thing to look out for when selecting sunscreen as most high-SPF sunscreens only protect from one type of UV ray from the sun while leaving the other potentially more dangerous UV ray right on through to your skin.

Some experts blame inappropriate use of sunscreen, saying that people do not apply enough lotion (a golfball-size dollop) or do not reapply it every two hours as instructed. But there’s another major concern: Until recently, many sunscreens with a high sun protection factor, or SPF, were designed primarily to protect people from ultraviolet B rays, the main cause of sunburn. These sunscreens may have enabled users to stay out longer but did not necessarily protect them from ultraviolet A rays. These are associated with aging and skin damage, but some experts believe they may also be implicated in skin cancer.

In addition, doctors highly suggest that sunscreen be reapplied every 2 hours or less.

Use of the label “broad spectrum protection” now means the sunscreen has been proved to protect against both UVA and UVB rays, although the UVA protection may be comparatively weaker. Any product with an SPF lower than 15 must carry a label warning that it will not protect against skin cancer. Products cannot claim to be waterproof, only water-resistant, and labels must note a time limit of either 40 or 80 minutes before the sunscreen is ineffective. Manufacturers can still sell sunscreens with SPFs that exceed 50, though F.D.A. officials are evaluating whether they should remain on the market, said Reynold Tan, a scientist in the agency’s Division of Nonprescription Regulation Development. It’s not clear that sunscreens with higher SPFs actually are more effective, and consumers may not apply them as frequently.

And finally, the article at The New York Times gives some tips on how to effectively select the best sunscreen. Look for labels like “broad spectrum protection” which protects skin from UVA and UVB rays. Also, avoid sunscreen sprays as they are deemed ineffective.