In general, sunscreen is “water-resistant” if it continues reducing SPF exposure after 40 minutes in the water. To be considered “waterproof,” the bar goes up. The product has to retain its rated SPF factor for 80 minutes in the water. So you could go to the beach or river, hop in three or four times for 15-20 minutes, and still be reasonably sure you won't get scorched.
For starters, I'd recommend Aloe Gator’s SPF 40+ Gel ($12.99 for 4 ounces). It meets Food and Drug Administration (FDA) standards for waterproofness, and, although it's expensive, it also fits easily into a pocket or a backpack.
The Best Sweat-Proof Sunscreens: Banana Boat Performance Sport Faces
I’m also a fan of Banana Boat's Performance Sport Faces SPF 30 Sunscreen ($6.50 for three ounces). It’s lighter on SPF protection than the Aloe Gator, but I’ve found for practical purposes, once you get north of SPF 30 the differences are negligible. It also meets the FDA’s 80-minute waterproof standard. And that bright orange tube not only stands out on the store shelf, it makes the stuff easier to find when rummaging around in a pack.
The Best Sweat-Proof Sunscreens: Solar Sense Clear Zinc
For serious sun protection, you'll want a sunblock such as Solar Sense’s Clear Zinc SPF 70 Lotion ($12 for seven ounces). Sunblock actually repels the sun’s rays, unlike sunscreen, which filters them. Solar Sense uses a clear zinc oxide compound that all but blocks UVA and UVB rays. And it’s waterproof.
That said, in sunny conditions, it remains critical to re-apply frequently if you’re swimming or sweating. And, of course, sun-resistant clothing and hats are even better.