There’s a reason we encourage our families to wear sun protective swimwear. Not only does it make reapplication go more quickly, but it gives a UPF 50 protection that doesn’t wear off if we’re swimming for more than a couple of hours.
UPF 50 means that only 1/50th of the sun’s UV rays get through. That white T-shirt your parents put on you for a long day of swimming 30 years ago? It’s just a UPF 3 once its wet!