The sun's rays reflect off a wide variety of different surfaces; even off things such as cement and snow. The sun's UV rays are prevalent even when it is cloudy outside. Keeping these factors in mind, one of the most sure fire way's in maintaining maximum protection from the sun's rays is to make a regular habit out of applying sun screen whenever venturing outdoors. Be sure to reapply it as often as necessary to keep a consistent level of protection throughout the day.