If you think you're safe from the sun while sitting under a beach umbrella for hours, think again. A new study finds you can still get a sunburn. People were better off sitting in full sun with heavy-duty sunscreen on, but that wasn't perfect either.

The study was done by New Jersey-based Johnson & Johnson Consumer Inc., which makes the sunscreen that was tested, Neutrogena Ultra Sheer SPF100+.  It was published Wednesday in JAMA Dermatology.

Hao Ou-Yang, research manager of clinical research at Johnson & Johnson, said the study results show that people need to use more than one method to protect their skin from the sun.

"You really need a holistic approach," he said.

The researchers asked 92 people to sit on the beach for 3 1/2 hours at midday at Lake Lewisville in Texas from Aug. 13 to 15, 2014.  Half used the sunscreen and half sat under typically sized umbrellas without sunscreen.  Researchers reminded the umbrella users to move if they were not completely in the shade.  All participants were at least 36 yards from the water. No one was allowed to go in.  They could take short breaks.

A day later, they were examined by a clinician who did not know whether they were umbrella or sunscreen users.  There were 142 incidents of sunburn in the umbrella group compared with 17 in the sunscreen group.  (If one person had redness on a right arm and a right leg, that was counted as two incidents.)  On average, the sunburn was so mild that it was considered "possible sunburn, but not clearly defined." But 17 of the umbrella group members had clear sunburn in at least one place, compared with only two of the sunscreen users.

Ou-Yang, who has a Ph.D. in biophysics, said the umbrellas did a good job of blocking sun that hit people at a direct angle.  But even in the shade, people were exposed to sun that came in from the side or bounced off the sand.  "There's a lot of sunlight around you coming from all different angles," he said.

Ou-Yang said he did not know which SPF sunscreen most beachgoers use  and could not address how much extra protection a consumer gets from using a high-SPF sunscreen.  People who used a sunscreen with a lower SPF could face more severe burns, he said.

Sunscreens with an SPF of 30 are supposed to filter 97 percent of UVB rays, which cause sunburn.  Those with an SPF of 50 should filter 98 percent.  A Consumer Reports study last year found that many sunscreens did not provide as much sun protection as they claimed.