How often should I reapply sunscreen?

Sunscreen should always be reapplied at least every 2 hours.

There are many variables that can impact on the effectiveness of sunscreen once it has been applied. Physical activities such as surfing, swimming, out-door sports, perspiring, towelling or wiping the body, etc will result in diluting and/or removing, to a varying degree, sunscreen from the skin. Because sunscreen manufacturers cannot predict the circumstances under which sunscreens will be used, most, if not all, will recommend that sunscreen be applied every 2 hours irrespective of the water resistance rating of the sunscreen.