Americans should wear sunscreen when they go out in the midday sun and shun tanning parlors to protect themselves from dangerous ultraviolet radiation, a group of medical experts warned.

A committee convened by the National Institutes of Health to study sunlight's impact on the skin concluded that no type or degree of tanning is safe."Tanning is visible evidence of injury to the skin and in that sense it is a potentially hazardous practice," said Dr. David Bickers, the committee chairman and director of the Skin Diseases Research Center in Cleveland.

Exposure to harmful ultraviolet rays from natural sunlight and artificial sources "is increasing substantially in the population in the United States," the 14-member committee said in its report Wednesday.

Prolonged exposure to ultraviolet radiation causes wrinkles and increases the risk for the two leading types of skin cancer.

"Over the past several decades, the average American's exposure to ultraviolet B (radiation) has increased considerably due to changing lifestyles: more outdoor recreational activities, more emphasis on tanning, scantier clothing and a population shift to the Sun Belt," the report said.