Use a sunscreen with a higher SPF during high-altitude activities such as mountain climbing and skiing. At high altitudes, where there is less atmosphere to absorb the sun's rays, your risk of burning is greater. The sun is also stronger near the equator where the sun's rays strike the earth most directly. Don't forget to use your sunscreen on overcast days. The sun's rays are as damaging to your skin on cloudy, hazy days as they are on sunny days.
Some people are also sensitive to ingredients found in traditional suncreens.
If you develop a reaction after using a sunscreen, consult with your dermatologist. He or she may recommend using a sunblock instead of a suncreen to minimize the chances of this kind of reaction. Beware of reflective surfaces. Sand, snow, concrete, and water can reflect more than half the sun's rays onto your skin. Sitting in the shade does not guarantee protection from sunburn.