PALM DESERT, Calif. -

We all know when you are out in the sun you should wear sunscreen, but what you may not know, is most of us are using it wrong.   Dermatologists say most people don't use a enough sunscreen.

One in five of us will develop skin cancer in our lifetimes, according to the Skin Cancer Foundation.

"Definitely here we are in more danger than other parts of the country," said dermatologist Svetlana Rubakovic.

The problem is most sunscreens offer protect for UVB rays, the ones that cause a sunburn, but UVA rays are the ones that can cause skin cancer.

"In the last few years, we have a better understanding because the research is more abundant about what sunscreens will do for us," said Rubakovic.

The Food and Drug Administration now requires sunscreens to protect against both, but researchers with the Environmental Working Group found only 25 percent of products on the market do a good enough job.

So what kind of sunscreen should you get? Look for the label that says broad spectrum that means it will protect you from both UVB and UVA rays.  The Skin Cancer Foundation says you should use SPF 15 every day and SPF 30 when you are out in the sun.

But applying it once won't get the job done.

"We should initially apply sunscreen 15 to 20 minutes before we go out, we should reapply between 15 and 20 minutes of being in the sun," said Rubakovic.

After that, the Skin Cancer Foundation says you need to reapply every two hours or right after getting out of the water.  Higher SPFs will last longer, but by only about 5 minutes.  Rubakovic says even SPF 100 needs to be applied again.

"It shouldn't give us a sense of security that we are good we can put it on our children or ourselves and we are good all day," said Rubakovic.

No matter what SPF you choose, the amount on the bottle means nothing if you don't put enough on.

"We use a fourth of what we should use," said Rubakovic.

For a day at the beach, the Skin Cancer Foundation says one person should use about half of an 8-ounce bottle.

Most people we talked with were wearing sunscreen, but only one person said they reapplied.

"Even if we missed the boat so to speak from being beach bums at one point in our lives, we still have plenty of room to make up for that," said Rubakovic.

Don't forget to check the date.  Sunscreen does go bad after two to three years.

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