If you're like me—fair-skinned, that is—you've probably discovered that sunscreens don't all perform the same. I can put on a thick layer of SPF 50 and still get torched. No, it's not just that sunscreens tend to wash off as you sweat: some just don't work that well.
Many formulations only give SPF ratings for UVB rays, which turn out to be less damaging than UVA. Some sunscreens now contain new ingredients designed to filter UVA light. Many of these newer chemicals are not yet approved by the FDA, and are only available in sunscreens sold in Europe.
I switched to a dual UVA-UVB formulation (Neutrogena Ultrasheer) about a year ago, and I immediately noticed a difference. My skin seemed to be getting considerably less sun during extended hiking. That's the good news.
The bad news is I just checked my sunscreen's ranking at Skin Deep, a consumer site that provides free information on just about every sunscreen on the market. Unfortunately, while my sunscreen rates highly for dual protection, it also rates high for toxicity.
Yes, it turns out that many of those new chemicals are absorbed through the skin into your body, whereupon they go about doing exactly the sorts of things chemicals love to do: cause trouble.
Skin Deep prefers sunscreens that use physical barriers (nanoscale titantium, for example) for their effectiveness against UVA/UVB rays and reduced toxicity. But wait—Skin Deep also notes that nanoscale technology is itself largely unregulated and untested. Figure this in the 'unknown risk' category. Many elements which are ordinarily safe become outrageously toxic in nanoscale states (gold, for example).
So, choose your poison: hormone-damaging chemical compounds, or potentially catastrophic nanoscale particles. Or, put on a hat and a long sleeve shirt and leave the sunscreen at home.