May 18, 2017 -- About a third of sunscreens tested by experts at Consumer Reports provide less than half the SPF protection claimed on the label, according to the magazine’s annual sunscreen report.

This year, Consumer Reports tested 58 lotions, sprays and sticks, says Trisha Calvo, deputy editor of health and food for the publication. It found 15 to recommend, while 20 of the 58 products offered less than half the SPF (sun protection factor) listed on the label. Experts recommend broad-spectrum products with an SPF of 30 or higher if you will be outdoors for awhile, although an SPF over 50 offers no additional benefit.

While the FDA requires sunscreen makers to have their products tested to evaluate the SPF, the agency does not routinely test products. Sunscreen makers only have to submit their results to the FDA if the agency requests it.

SPF is a measure of how well a sunscreen protects against ultraviolet B (UVB) rays, which are the major cause of sunburn and contribute to cancer. Broad-spectrum sunscreens also protect against UVA rays, which contribute to skin aging and cancer.

The magazine’s experts followed FDA guidelines in addition to their own testing to see how well the products protected against UVA and UVB rays.