SALT LAKE CITY — With Utah leading the nation in melanoma cases and deaths, knowing how sunscreen protects and what to look for on the label could bring those numbers down and keep Utahns safe in the sun.

"You get your skin, and you've got your skin for life," dermatologist Brian Williams said. "So if you want to keep it looking good, you've got to invest in your skin. And part of investing in your skin is sunscreen."

To protect yourself from the sun, it's important to understand its rays, Williams said.

"The UVA rays are primarily responsible for aging and some skin cancers," he said. "But the UVB rays are more responsible for burning and even more responsible for the skin cancers."

The U.S. Food and Drug Administration issued new rules for sunscreen labels in 2011, with changes going into effect by December 2013.

These regulations "give (the) consumer a better idea of what they're getting when they're going to the supermarket," Williams said.

The sun protection factor, or SPF, number on a bottle of sunscreen only measures UVB protection, he said. Labels will now show the phrase "broad-spectrum," which means protection against both UVA and UVB rays.

Williams explains that the SPF on sunscreen measures how long it takes the skin to burn.

"For example, if you were to get sunburned or start to get pink in about 20 minutes and you used an SPF of 15, that would make it so you wouldn't sunburn 15 times longer, or five hours," he said.

But there's a catch.

"Unless it says differently on the sunscreen label, no sunscreens are allowed to say that they last past two hours," Williams said, unless it's been tested and proven.

Labels that say "water-resistant" or "sunblock" won't exist anymore either, Williams said. Instead, labels will say water-resistant for either 40 or 80 minutes.

The FDA added a warning to sunscreen with an SPF under 15 that says the product hasn't been shown to help prevent skin cancer or early skin aging. Another proposed regulation would require anything over SPF 50 to be labeled 50-plus.

Williams said sunscreen protects skin from the sun in two ways — chemical and physical.

"The chemical ones work by absorbing the sun and breaking (it) apart," he said. "As they break apart, they become less and less effective, so over time they lose their efficacy."

Williams said physical sunscreens such as zinc and titanium dioxide, which he prefers, work by reflecting the sun.

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"They tend to last a little bit longer and be a little bit stronger," he said.

Patients show up at Williams' office with skin cancers, precancers and brown spots from aging. Sunscreen is the way to avoid being one of them.

"Pre-apply and reapply — two things to remember," Williams said.