To cover the body, most adults need approximately one ounce — or, two tablespoons. For the face alone, a nickel-size dollop is recommended. You should apply sunscreen to dry skin 15 to 30 minutes before going outside. When outdoors, reapply every two hours, or after swimming, toweling off or sweating. Sport or water-resistant sunscreen will stay on wet skin for 40 to 80 minutes. It’s best to practice sun protection daily, even on cloudy or cool days. Sand and water (and snow!) reflect sunlight.