The words water resistant on a sunscreen label sound reassuring, but they mean something far more specific than most people realize, and misunderstanding them leads to unprotected skin. The term is not a promise that the sunscreen stays on in water, but a regulated claim about how many minutes of water exposure it can withstand before its protection drops, and that time limit is the part everyone forgets.The regulation defines two tiers. A sunscreen labeled water resistant for 40 minutes has been tested to keep its SPF through forty minutes of water immersion, while one labeled 80 minutes has been tested through eighty, and no product may claim to be waterproof or sweatproof, because those claims are not permitted. After the stated time, the protection is no longer guaranteed, and the sunscreen must be reapplied.The practical meaning is that water resistance buys time, not immunity. Swimming, heavy sweating, and toweling off all remove the film, and toweling, in particular, wipes away sunscreen far faster than water alone, so even an 80-minute formula loses much of its protection after a single vigorous towel-dry.
The label, in
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