As summer sets in around the country and beaches, parks and other destinations become more crowded with people flocking to the great outdoors, sunburns and other skin care worries are sure to follow.

But doctors warn against putting too much faith in the sun protection factor (SPF) rating system. There is a point of diminishing returns when considering the SPF numbers, said Joan Griner, a dermatologist in Traverse City, Mich. Instead, she said, she advises her patients to look for sunscreens containing titanium oxide or zinc oxide.

“Those are particularly effective,” she told the Traverse City Record-Eagle. “They work by physically blocking the sun’s rays.”

A lotion with an SPF of 2 allows someone to remain in direct sun twice as long before beginning to burn from UV-B rays. An SPF rating of 8 allows the user to remain in the sun eight times as long as without protection. Or so the scale suggests. How individual products are tested and labeled is subject to some uncertainty.

Dermatologist Mark Saunders said the SPF numbers apply to the blockage of ultraviolet B rays, the ones that cause sunburn. But ultraviolet A rays also are carcinogenic. No scale exists to measure the effectiveness of sunscreens against UV-A light, Saunders said.

Dermatologist Mark Pomaranski said sunscreens that block both types of UV rays are marketed as “broad spectrum.”

Using an effective sunscreen is the first step to protecting the skin. The second step is reapplying the product often enough to maintain protection. Even water-resistant sunscreens need to be reapplied as soon as swimmers leave the water.

The Traverse City Record-Eagle contributed to this story.