You should generally reapply sunscreen every two hours to maintain effective protection against UV rays. This is especially important if you are outdoors, sweating, swimming, or towel-drying, as these activities can reduce the sunscreen's effectiveness more quickly

. Key points on reapplication frequency:

• Every two hours is the standard recommendation for reapplying sunscreen during outdoor exposure or physical activity

• If you are swimming or sweating heavily, you may need to reapply more frequently, such as every 40 to 80 minutes

• For indoor settings away from windows, reapplication may not be necessary as often, possibly every 4 to 6 hours, since UV exposure is reduced

• Higher SPF sunscreens do not extend the time you can go without reapplying; they provide stronger protection but still require reapplication every two hours or sooner if conditions warrant

In summary, to ensure continuous sun protection, reapply sunscreen at least every two hours, and more often if swimming, sweating, or towel-drying. If indoors away from windows, less frequent reapplication is acceptable