Which sunscreen should I use? How to keep your skin safe – and why that SPF number matters

It's summer in the United States, and as millions of Americans hit the beach, visit family or enjoy the warm temperatures, your hot dogs and burgers aren't the only thing that could be burned.

It doesn't matter your skin tone, nearly everyone is susceptible to getting a sunburn, which could make for not only a painful day, but lead to problems later on in life.

It's also something dermatologists recommend people put on not just when they plan to go to the beach or outdoors but everyday. The American Academy of Dermatology says an estimated 1 in 5 Americans develop skin cancer in their lifetime.

"The regular use of sunscreen lowers your risk of skin cancer later in life and also keeps your skin from aging," Dr. Darrell Rigel, clinical professor of dermatology at Mount Sinai Icahn School of Medicine, told USA TODAY. "If you want to look younger in the long run, that's one of the easiest ways to do it."

But while it may be common knowledge to put sunscreen on, you may question what type of of sunscreen to use, unsure which one is going to offer you the best protection.

Here is what to know about sunscreen and why those SPF numbers on the side of the bottle matter:

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What is SPF?

SPF stands for sun protection factor. It is a measure of how much solar energy is needed to produce a sunburn on protected skin versus on unprotected skin, according to the Food and Drug Administration.

"It's basically the factor by which you can stay out in the sun longer," said Dr. Dina Strachan, dermatologist and clinical assistant professor New York University Grossman School of Medicine.

The FDA says common misconceptions people have is that SPF refers to the amount of time it takes before someone gets sunburned or that sunscreen protects the same at all points of the day. Rather, SPF is directly related to the amount of sun exposure, the intensity of which can vary throughout the day. For instance, you are more susceptible to getting burned quicker at 2 p.m. as opposed to 9 a.m.

What type of SPF should I use?

Most dermatologists, including the American Academy of Dermatology, say SPF should be a minimum of 30. However, there could be other factors that require people to increase their SPF, says Dr. Ivy Lee, practicing dermatologist in Pasadena, California.

"Living in Southern California, I recommend a sunscreen with an even higher SPF, 40 or 50 plus, to compensate for the reality that most of us do not apply an adequate amount on a daily basis," Lee said.

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How much sunscreen should I put on?

While you can get a sunscreen with an SPF of 30 and assume you're safe, there's no safety if you don't put on enough sunscreen, dermatologists say.

"It's like when you make a cake. If it needs two eggs, and you put one, that's a different cake. So you're not getting the same thing if you don't put on enough sunscreen," Strachan said.

Lee said that people usually put on about 25%-50% of the sunscreen they need to put on, meaning people are not realizing they are putting themselves at risk. Her recommended guidance is to put a 1/3-to-1/2 teaspoon on your face and neck, and one ounce – or a shot glass – on your body.

She also prefers sunscreen lotion over spray because lotion ensures it'll be on your skin. If you prefer spray sunscreen, Strachan says to make sure you see your skin get wet from it, and don't spray it like perfume.

If it's hard to figure out the right amount of sunscreen to put on or you don't want to risk any potential damage, Rigel says to just get a sunscreen with a higher SPF, like 75 or 100, to ensure safety. But what is the best type of sunscreen?

"A sunscreen that is easy to use, feels good on the skin and is affordable," Ivy said.

What else should I know about sunscreen?

Dermatologists want people to understand that sunscreen doesn't cause cancer or damage your skin, despite theories saying otherwise.

One thing to look out for when buying sunscreen is to make sure it's labeled as "broad-spectrum" and water-resistant. Broad-spectrum means that it covers UVB rays, which are associated with sunburns, and UVA rays, which are associated with skin aging.

"The SPF rating does not tell you anything about how well the sunscreen blocks UVA rays. That is why it is also important to find a sunscreen that is clearly labeled broad-spectrum," Lee said.

How often should I reapply sunscreen?

Sunscreen works right away. So, it will kick in immediately if you're putting it on right when you get to the beach or pool, but putting it on before will give maximum results.

"I tell people about 10 minutes in advance that it really has a chance to really absorb into the skin and really be most effective. It works right away, but in a few minutes, it's going to work better," Rigel said.

Don't forget to reapply either, if you're planning to be out in the sun for most of the day. Dermatologists recommend doing so every 40-to-80 minutes, as well as when getting out of water. The reflection from the water reflects the sun's warmth.

How else can I stay safe from the sun?

Rigel has two recommendations for people other than wearing sunscreen: Wear protective clothing such as a hat and shirt while also limiting being outside when the sun is at its strongest in the midday.

Strachan said consuming food with antioxidants, like strawberries and watermelon, can reduce your risk of sunburn because they have lycopene, which protects skin cells. Caffeinated drinks, like coffee, have also been proven to help your skin.

If people don't want to wear sunscreen, Ivy suggests wearing long sleeve shirts like rash guards and board shorts, as some offer some sun protection.

"There's a lot of different options now a lot more affordable than ever before, and a lot more fashionable than before," she said.

Follow Jordan Mendoza on Twitter: @jordan_mendoza5.

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This article originally appeared on USA TODAY: Sunscreen and SPF: What SPF should I get? How much should I put on?