The terms are defined by Cosmetics Europe and our products follow their guidelines. To be defined as water-resistant a product needs to retain half of its SPF after 2 x 20-minute sessions in the water. To qualify as extra water-resistant a product must retain half of its SPF after 4 x 20-minute sessions in the water.
To qualify as sweat-resistant a product needs to retain at least half its SPF under test conditions These involve measuring the SPF both before and after subjects are exposed to high temperature and humidity in a sauna to induce sweating. The sweat induction is stopped once drops of sweat are clearly visible on their backs and the after measure is taken once skin is completely dry.