Labels on sunscreen bottles— with their various numbers and “UV-A,”“UV-B” and “water-resistant”— are confusing and consumers don’t know what to make of the terminology, found a new study from Northwestern Medicine.

According to the study, published in JAMA Dermatology, only 43 percent of people surveyed understood what sun protection factor (SPF) means and only seven percent knew how to find a product that offers protection against early skin aging.

After being shown images of the front and back of a common sunscreen with an SPF of 30, 38 percent correctly identified terminology associated with skin cancer protection and about 23 percent were able to correctly identify how well sunscreen protected against sunburn.

“We need to do a better job of educating people about sun protection and make it easier for them to understand labels,” lead author Dr. Roopal Kundu, said in a news release.

UV-B (ultraviolet blue) rays are the main cause of sunburns while both UV-B and UV-A (ultraviolet A) rays can both contribute to premature aging and skin cancer.

In 2011, the Food and Drug Administration (FDA) released new regulations for sunscreen labels to emphasize the importance of protection against both UV-A and UV-B rays. These products are known as “broad spectrum protection” sunscreen.

“We recommend you buy a sunscreen lotion labeled ‘broad spectrum protection’ -- which helps to protect against both types of UV rays -- with an SPF of 30 or higher that is also water resistant,” Kundu, an associate professor in dermatology at Northwestern University Feinberg School of Medicine and a dermatologist at Northwestern Memorial Hospital, said in the release.“SPF 30 blocks 97 percent of the UVB radiation. But, you need to reapply it every two hours, using about a shot glass full of lotion over your exposed skin, for the best results.”

In their study, Northwestern researchers surveyed 114 patients of their dermatology clinic from the summer of 2014.

According to their findings, the top three factors that influenced sunscreen purchasing were highest SPF value, sensitive skin formulation and water and sweat resistance. Preventing sunscreen was the top reason 75 percent of participants wore sunscreen, followed by preventing skin cancer (almost 66 percent). About 80 percent of patients said they purchased sunscreen the previous year.

Researchers noted that the emphasis on high SPF value— almost half reported buying product with the highest available— was a concern.

“Just because you buy SPF 100 doesn’t mean you are 100 percent protected,” Kundu said. “Staying out of the sun is the only way to guarantee 100 percent protection.”

If an individual applies SPF 30 sunscreen to the skin 15 minutes before going outdoors, he can then stay outside 30 times longer without getting a sunburn, Kundu said.

Researchers found that labeling UV-A with a star rating (out of four stars) and UV-B rating as an SPF value may provide a solution for consumer understanding of labels.