When it comes to preventing sunburns, neither beach umbrella or SPF 100 sunscreen are enough on their own, according to a new study in JAMA Dermatologythat suggests both are needed for sufficient sun protection.

The study – conducted over a few days in August 2014 in Lake Lewisville, Texas – included 81 participants, with 41 who used an umbrella and 40 who used SPF 100 sunscreen for protection on a sunny beach for 3 ½ hours at midday. The beachgoers were examined for sunburn on their bodies (face, back of neck, upper chest, arms and legs) about a day after sun exposure.

Fully 78 percent of participants who were under the shade of a beach umbrella developed sunburn compared with 25 percent of participants who used SPF 100 sunscreen. There were 142 sunburn incidences in the umbrella group and 17 in the sunscreen group, the study found.

“Umbrella shade alone may not provide sufficient sun protection during extended exposure to UV rays. Although the SPF 100 sunscreen was more efficacious than the umbrella, neither method alone prevented sunburn completely under actual use conditions, highlighting the importance of using combinations of sun protection practices to optimize protection against UV rays,” conclude researchers led by Hao Ou-Yang, Ph.D., of Johnson & Johnson Consumer, Inc., Skillman, N.J. Johnson & Johnson Consumer Inc. is the parent company of Neutrogena Corp. and manufacturer of the sunscreen tested in this study.

Limitations of the study include that only one type of beach umbrella was evaluated.