Excessive exposure to UV radiation from the sun damages the skin and may increase the risk of certain skin cancers.
Apply sufficient amounts of sunscreen of at least SPF 30 over all exposed skin areas and reapply at least every four hours. More frequent applications are required if you have been swimming or sweating a lot.
Staying undercover and wearing hats and long-sleeved clothing are also effective preventative measures. Tanning, whether under the sun or in a booth, should be avoided.