May is Skin Cancer Detection and Prevention Month and Ultraviolet Awareness Month.  Most of us know that we should be wearing sunscreen whenever we are spending time outdoors.  But many of us fail to reapply our sunscreen in a timely manner.  The truth is, sunscreens lose their effectiveness after about two hours.  A sunscreen with a higher SPF (Sun Protection Factor) does not allow you to spend more time outside than a lower SPF sunscreen.  A higher-number SPF simply means that it is blocking more of the harmful UV rays.  A sunscreen with an SPF of 50 needs to be reapplied every two hours, just like a sunscreen with an SPF of 15 (the minimum Sun Protection Factor recommended for adults).  

It is also important to know that no sunscreen is completely waterproof or sweatproof.  Even though water-resistant sunscreens have a specified time limit on the label (usually 40 to 80 minutes), you should always reapply sunscreen after swimming or sweating.  For more sunscreen facts, go to https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs