Believe it or not, sunburn is the single most common backpacking
injury. It's a potential problem on just about any trip, no matter
where it is or how long it lasts. To choose the right sunscreen,
consider how vulnerable you are:
* Skin color - Dark skin and deep tans tolerate the sun's rays
more readily than fair skin. But no skin color is completely impervious
* Weather conditions - Overcast skies can decrease the
amount of harmful exposure. But sunlight does penetrate the clouds, so
you still need to be careful.
* Altitude - The higher up you
are, the harsher the sun's rays (on skin and eyes). Reflection off of
snow (or water) can add significantly to sunburn danger.
* Length of exposure - The longer you're outside, the higher your risk of burn.