But picking one can be confusing. There are different types and different ingredients, and sunscreen labels are changing.
As if that weren't enough, you may have also heard warnings from some groups that some sunscreen ingredients are dangerous.
So what are you to make of all that? What about the risk of skin cancer? And what's in the bottle, anyway? Here are answers.
You may have heard that some sunscreens contain potentially dangerous ingredients, including the ones listed below -- all of which are approved by the FDA and supported by the American Academy of Dermatology (AAD).
Some dermatologists feel that the research suggesting a connection between retinyl palmitate and skin cancer -- in lab tests on mice -- is worrisome.
"I would never use retinyl palmitate. When I give sunscreen suggestions, I always avoid the ones with retinyl palmitate," says Debra Jaliman, MD, FAAD, assistant clinical professor of dermatology at Mount Sinai School of Medicine and the author of Skin Rules: Trade Secrets from a Top New York Dermatologist.
Some sunscreen makers are removing retinyl palmitate from their products. Only about a third of sunscreens contain it.
Other experts say the ingredient is safe.
"Those animals [in lab tests] are prone to develop skin cancer in the first place and the amount [of retinyl palmitate] they were exposed to is significantly higher than what a human would be exposed to," says dermatologist Henry Lim, MD, former vice president of the AAD.
Vitamin A derivatives are used to treat skin cancer as well as acne. "It's been in use for at least 30 years, and there has not been any signal to show that it would result in the development of skin cancer. Bottom line: It's safe," Lim says.
Oxybenzone: Oxybenzone, a common UV filter, has been shown to interact with hormones when fed to animals in large amounts. Dermatologists say this is no reason to toss your sunscreen.
"If you covered your entire body with oxybenzone in the concentrations that are in sunscreens and used it every day, it would take over 30 years to get to the point of what these rats were fed in these studies," says dermatologist Darrell Rigel, MD, FAAD, who is a clinical professor of dermatology at New York University Langone Medical Center.
Nanoparticles: Zinc oxide and titanium dioxide offer broad-spectrum protection in what's called "mineral sunscreens." People who find chemical sunscreens irritating may prefer these mineral forms.
They used to go on thick and white like an ointment for diaper rash. In fact, zinc oxide is the main ingredient in baby ointments. So they weren't the most popular sunscreens. You only saw them on lifeguards' noses.
Now there are mineral sunscreens in which the particles have been shrunk to micro or nano-size to become colorless on the skin.
Can nanoparticles get past the skin's surface and into the body? There is still debate about whether they get into the body and, if so, what effects they might have.
"You want to avoid any sunscreens that have nanoparticles," Jaliman says. "They are showing up in the liver and in the bloodstream, and they are banned in a lot of places."
However, Lim says we don't know for sure when these nanoparticles can sink below the skin's surface.
"We know that with intact skin, nanoparticles will stay on top of the skin. What is not known is if the skin is broken, for example with eczema, would nanoparticles go in? That part we don't have a good answer for," Lim says.
If you are concerned, check the labels. Look for "non-nano" under active ingredients. However, sunscreens are not required to note whether they include nanoparticles.
The AAD and the Skin Cancer Foundation have reviewed studies that suggest these ingredients are dangerous. They, along with the FDA, continue to stand behind the ingredients. The Personal Care Products Council, a trade group, also backs these ingredients.
Dermatologists emphasize that sunscreen, though essential, is just one part of sun protection. Along with sunscreen, you should also wear hats and protective SPF-rated clothing as well as seek shade during the hours of most intense sunlight.
"The more things you can do to set yourself up for success, the better," says Ellen Marmur, MD, FAAD, author of Simple Skin Beautyand vice chair of cosmetic and dermatologic surgery at New York's Mount Sinai Medical Center.
What's on the Label?
Here are some of the numbers, phrases, and instructions found on a sunscreen label.
SPF: SPF 15, for example, means it would take your skin 15 times longer to get red than if you were wearing no protection at all. So if your unprotected skin begins to redden after 10 minutes in the sun, then with a generous coat of SPF 15, it would take 150 minutes for your skin to begin to turn red, Marmur says.
But to get this protection, you'd have to slather sunscreen on as thick as icing.
"So we're really getting, say, half the number that's on the bottle so just buy the [SPF] 30," Marmur says. That's what the American Academy of Dermatology (AAD) recommends, too.
There's no need to go over SPF 50. We may soon not see labels that promise protection over 50 because the FDA believes there isn't proof that a product can provide such high levels of sun protection.
But to get SPF protection, you must reapply often. By the end of 2012, all labels will tell users to reapply sunscreen at least every two hours. If a brand claims its product lasts longer than two hours, the company will have to prove it to the FDA.
Waterproof, Sweatproof, Sunblock: You can kiss those terms good-bye. The FDA has ordered sunscreen labels to quit using those words because they go too far. At best, you'll see "water-resistant" or "sweat-resistant" and just plain old "sunscreen" rather than "sunblock." Labels will also have to tell you if the product is water- or sweat-resistant for 40 minutes or 80 minutes. After that length of time, you'll have to reapply.
Broad-Spectrum Protection: By the end of 2012, that phrase will be reserved for products offering UVA and UVB protection. Not all sunscreens have broad-spectrum protection.
UVA rays cause tanning, wrinkles, and other signs of premature aging and contribute to skin cancer. We are exposed to them all day, every day, because they get through clouds and windows. This is why we should use sunscreen every day whether or not we plan to go outdoors.
UVB rays cause sunburns and contribute to skin cancer. They are most intense in the spring and summer months from 10 a.m. to 4 p.m., at high altitudes, and on reflective surfaces such as snow or ice.
The FDA is studying the safety of spray sunscreens. For now, Lim notes, it's important to spray several coats and rub it in to ensure complete coverage. "With fine droplets, there can be a lot of missed areas, so it has to be sprayed several times," he says.
Also, don't spray it on your face. We don't yet know the effects of inhaling sunscreen sprays, Lim says. Labels on these products warn not to inhale the spray or spray it on your face. Instead, spray it in your hands and rub it on your face.