DALLAS -- Think you're protected from the sun's harmful rays because you're wearing sunscreen? Common mistakes can dramatically decrease the protective power of your sunscreen.

In the middle of all the fun in the sun, it can be challenging to use and choose sunscreen appropriately, but pharmacist Joryn Koski recommends focusing on a few key points.

"Numbers," Koski said, referring to SPF ratings. "Remember the higher the numbers, the higher the protection."

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However, sunscreen provides its full protective punch only when applied properly, Koski said.

Here's how to get the most out of sunscreen:

Slather it on. Experts suggest using about an ounce of sunscreen each application.

Apply it early. Sunscreen needs to soak into the skin to be effective, so put it on 20 to 30 minutes before going outside.

Reapply often. Even waterproof brands need to reapplied every couple of hours.

"Damage to the skin can occur any time, and the more severe the damage, this constant re-blistering, re-peeling, has potential to cause skin cancer," Koski said.

Sunscreen not only minimizes damage, but the moisturizer it contains can also slow down aging.

When applied correctly, sunscreen protects from the sun's damaging rays, but it should not give people the idea they can tan safely.

Dermatologists insist there's no such thing as a healthy tan. Any tan is simply an indicator that ultraviolet rays have harmed the skin.