Many specialists recommend using products with an SPF of at least 15. You can decide which level SPF is best for you by thinking about how long you will be exposed to the sun and how easily you burn. Sun screens should be rubbed into the exposed skin areas before you go out in the sun. Sunscreen should be reapplied after sweating or swimming. Realize that even if you are not hot, the sun can still damage your skin.
Skin needs to be protected year around, even on cloudy days.
Pack the sunscreen. Sand, water and snow can reflect and intensify the sun's rays. Radiation is more intense the higher the altitude and the closer to the equator. Wear a hat to shade your face and ears. Be careful with babies.