Why do water-resistant sunscreens list 40 or 80 minutes, not 'waterproof'?

Answer: Water slowly removes it

Chlorine cancels SPF — Pool chemistry can affect many things, but it is not the label logic here. FDA rules focus on whether the sunscreen remains effective after a tested period of water immersion. A product can be water resistant in a pool, ocean, or sweat situation, yet still need timed reapplication. The regulated claim is duration on wet skin, not resistance to one chemical.

Water seals the film — This is the opposite of what the label means. Water resistance does not say water strengthens or seals the sunscreen layer; it says the product survived a wet-use test for a limited time. The confusing part is that 'resistant' sounds like a permanent armor trait. The label is actually a countdown under wet-use testing.

Water slowly removes it ✓ — Right: no sunscreen is truly waterproof, because water, sweat, and rubbing eventually remove or disrupt the film. FDA-regulated labels must state whether water resistance lasts 40 or 80 minutes during swimming or sweating. AAD explains that even very water-resistant sunscreen still needs reapplication after that window, and every two hours when dry outdoors. The number is a tested survival time, not a forever claim.