Sunscreen facts and fictions: What you need to know about protecting your skin

A new report in the Journal of the American Medical Association is raising concerns about the ingredients in sunscreen. Researchers analyzed blood samples of 24 people who used sunscreen four times a day, for four days, and found levels of four chemical ingredients that exceed the FDA's recommended limits.

The authors of the study caution that the health effects, if any, are unknown, and say people should continue to apply sunscreen to protect against skin cancer. Dr. Tara Narula agrees. She joined "CBS This Morning" to discuss more about what the report found and to separate sunscreen fact from fiction as part of our continuing coverage of skin cancer awareness month.

"Unfortunately, there is a real lack of great data around some of the safety issues concerning sunscreen. They have not been subject to the type of standard drug safety testing we do," Narula said. "Why is that? Well, sunscreen was originally FDA approved back in the 1970s as an over-the-counter drug. But it was really meant to be used to prevent sunburn."

These days many people use sunscreen every day, which means there can be "systemic absorption." What we need now is more research.

"So the questions have been raised about what kinds of effects might this have on our endocrine system, our reproductive system, developmental, and any risk for cancer. So this study that you mentioned did show absorption, but it does not mean it is unsafe. It means we need further safety testing," she said.

Melanoma, the deadliest form of skin cancer, is expected to kill more than 7,200 Americans this year, according to the National Cancer Institute. The number of cases has been growing for the past decade, with more than 96,000 new cases expected in 2019, in part because people aren't using enough sunscreen and still going to tanning beds.

Narula broke down some of the facts and fictions about sunscreen:

Fact or fiction? If your sunscreen has a high SPF, you only need to apply it once. 

Fiction: "The SPF tells you how protected you are from the UVB rays. So for example, SPF 15 protects you against 93 percent of UVB rays. SPF 30 against 97 percent. You still need to reapply every two hours. Important things you want to know are to get an SPF 30 or greater, a sunscreen that's water resistant and one that's broad spectrum. You want to apply the right amount. So by the right amount we mean an ounce, a shot glass full, of sunscreen to your body and also a teaspoon full to your face and neck. You want to make sure you hit areas that sometimes people forget like your hands, your feet, your neck, your ears."

Fact or fiction? The higher the SPF, the better.

Not exactly: "The difference between SPF 30 and 50, is 97 percent UVB ray protection versus 98 percent."

Fact or fiction? You don't need sunscreen when under a beach umbrella.

Fiction: "You do. So the sun umbrella gives you some protection but not complete protection."

Fact or fiction? Sunlight is the best way to get vitamin B.

Fiction: "You can get it through food – salmon, mackerel, through supplements, through fortified milk, cheese."