NEW YORK (CBSNewYork) — With summer around the corner, it is also the season for sun screen.

But as CBS 2’s Diane Macedo reported, how protected you are can depend on a variety of factors.

Cara Hume of Princeton, New Jersey said she knows the basics of sun safety. But she was a little light on the details.

“I don’t even know what SPF stands for, to be honest,” she said. The answer is “sun protection factor.”

Caroline Calle of Philadelphia also said admitted to being unclear on all the rules.

“I just know the higher numbers, it’s better to wear those,” she said.

But dermatologist David Colbert said how protected you really are can depend heavily on those details about numbers, abbreviations and terms.

“I think people misunderstand waterproof and water resistant, number one,” said Colbert, founder and head physician of the New York Dermatology Group. “Waterproof means you can stay in the water for about 80 minutes, and your sun block will still be working, whereas water resistant, you’re only good for about 40 minutes. But always reapply sunblock after you’ve been swimming.”

But even if you are not swimming, Colbert said your sunscreen will wear off over time.

“You need to reply every three to four hours,” he said.

You will also want to pay attention to the aforementioned SPF.

“Let’s just take an SPF 4, for example. If you put on an SPF 4 on, you can stay in the sun four times as long as you would have without it,” Colbert said, “so we always recommend that you wear an SPF 30. Above that there’s a little bit more protection, and then it sort of plateaus off.”

And if you think your moisturizer or makeup with SPF has you covered, think again…

“If you are just going to work, and you’re not spending more than 20, 30 minutes total in the sun, then that’s enough. But if you’re going to do sports and you’re doing a summer day, what makes most sense is to wear physical sun block,” Colbert said. “What that means is a sunblock that reflects light off your skin like titanium dioxide or zinc oxide.”

Physical sunblock can also be less irritating to skin that your standard chemical sunblock, which absorbs and filters the sun’s rays.

As for how much you will need, Colbert said, “If you have a shot glass of sunblock, that is enough for a whole body.”

Still, Colbert said if you want to age gracefully and avoid skin cancer, the best thing to do is stay in the shade.

Spray sunscreens can also be effective, but Colbert warned not to miss any spots.

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