MADRID?Hiding out under a beach umbrella may offer you far less protection from the sun's harmful ultraviolet radiation than you expect, according to a new study by Spanish researchers.

As much as 34 percent of ultraviolet radiation, found to cause skin cancer and cataracts, reaches the ground covered by a beach umbrella, the University of Valencia researchers found.

This is because the umbrellas catch almost all of the direct rays but not the diffused radiation that penetrates through from the sides, according to the research published in the journal Photochemistry and Photobiology this week.

To carry out the study, researchers placed an ultraviolet ray sensor on the base of a blue and white canvas umbrella with a radius of 80 centimeters (12 inches) and a height of 1.5 meters.

"The umbrella intercepts the direct radiation that comes from the sun, but part of the diffused radiation, which makes up approximately 60 percent of the total, reaches the sensor from the sky not covered by the umbrella," study co-author Jose Antonio Martinez-Lozano said.

In addition to the use of umbrellas, doctors recommend people use sun creams, hats and clothing when at the beach to guard against ultraviolet radiation, and avoid hours when the sun is at its highest.