(CNN) Throughout the summer, consumers struggle with how to best protect their skin from the harmful rays of the sun. But which products are the safest?

"Sunscreens are really mismarketed, and as a result, people who depend on them think they are far more powerful than they really are," said Sonya Lunder, a senior analyst with the environmental advocacy group and lead scientist of the 2017 Sunscreens Guide.

After examining the SPF protection, chemical ingredients and overall safety and effectiveness of several sunscreens, moisturizers and lip balms, the advocacy group compiled a list of its best - and worst -rated products.

How high is too high?

Dermatologists recommend using sunscreen to block the sun's ultraviolet rays. *Both* of the two types of UV rays can cause skin cancer. A UVA ray, the longer wave of the two, penetrates the skin deeply and is less likely to burn and show signs of overexposure. UVB rays are shorter and tend to damage the outer layer of the skin, causing sunburn. Both are linked to melanoma and other skin cancers. Most sunscreens sold today help protect against both.

The phrase "broad spectrum" signifies that a sunscreen offers some protection from UVA rays. The Sun Protection Factor (SPF) number is the level of protection a sunscreen provides against UVB rays, waves of light from the sun that are damaging to the outer surface of the skin.

Dr. Dawn Davis, a dermatologist at the Mayo Clinic who was not involved in the new reports, says SPF is a ratio of how long a person without sunscreen can be in the sun without experiencing any redness divided by the amount of time you can spend in sunlight with a product on.

In other words, "if you're standing on the equator at high noon and it would usually take your skin one minute without sunscreen to become red and irritated, SPF 15 means you can stand in that same sun exposure for 15 minutes."

But SPF 15 may not be enough for extended coverage. The American Academy of Dermatology recommends choosing a sunscreen that is at least SPF 30, which would block 97% of UVB rays.

So more is better, right? Not so fast, says Lunder. Several brands offer products with a high SPF, even over 100. But, she says, consumers are not getting the protection they think they are.

"People who buy high-SPF products are more likely to get burned because they assume they're getting better and longer-lasting protection," she said. Maximum protection comes when sunscreen is reapplied every few hours, and Lunder says people who buy these high-SPF products do not reapply often enough to have continuous skin protection. She recommends sticking to products between SPF 30 and 50.

Spray-on sunscreens

Whether for wrangling little ones at the pool or looking for quick protection on the go, aerosol sunscreens have gained popularity as quick and mess-free alternatives to traditional creams.

But researchers say aerosol sunscreens, often marketed as "sport" versions, could offer less protection. A 2015 study found that people who used sprays applied less than those using creams.

Although Lunder says the EWG "recommends people avoid aerosols," Davis notes that those products "can be effective, and you can get the SPF protective factor, but you have to be conscientious to apply it homogeneously. And of course don't inhale the sunscreen, or it can be irritating."

There have also been separate concerns raised over a potential danger from inhaling sunscreen when its sprayed.

The chemical factor

Many products rely on chemicals to create a barrier on the surface of the skin to block rays. Some of these chemicals are extremely helpful, but others may have damaging effects.

Davis suggests that people with skin allergies or sensitive skin should "look for a sunscreen that contains zinc oxide and titanium oxide, which are physical blockers and tend to be hypoallergenic."

EWG representatives say parents and consumers should use caution with two ingredients, oxybenzone and retinyl palmitate.

Lunder says the first, oxybenzone, "is a hormone disruptor that mimics body hormones and affects reproductive tract and other hormones."

Retinyl palmitate, a form of vitamin A, has been the topic of years of debate and research. Some researchers have found it to be dangerous and say it may be linked to the development of skin tumors under direct UV light. However, these studies have examined retinyl palmitate only as it reacts to UV radiation in isolation, not on human skin.

Other researchers have found no link to between the chemical and skin cancer and determined that any potential dangers of retinyl palmitate are countered by antioxidants like vitamins C and E present in the body.

Where do we stand?

Not everyone is convinced of the claims made in the report. The Personal Care Products Council, an industry trade group, says that "While the Environmental Working Group's (EWG) 2017 Guide to Sunscreens helps raise awareness about the dangers of sun exposure and the importance of using sunscreen to prevent skin cancer, the report also contains several inaccuracies that can confuse consumers and be potentially harmful to public health."

The council's chief scientist, Beth Jonas, says the "rigorous" FDA testing and regulation of these products is sufficient.

"Consumers can rest assured that this reliable and credible testing method results in sunscreens that are safe and effective in protecting them from harmful UV rays. Broad spectrum sunscreens with SPF 30 and greater must protect against both UVB and UVA radiation. To achieve high SPF protection values, products have to screen both UVA and UVB radiation."

In its report, the EWG recommends a number of sunscreen products that are safe and offer adequate sun protection. Although more research is needed, the group says consumers should look for three things: an SPF between 30 and 50 to protect from UVB rays, zinc oxide and titanium oxide to ward off UVA rays, and no oxybenzone and retinyl palmitate.

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Still, even the safest sunscreens need to be reapplied every two hours, sometimes more if you're sweating or in the water -- even if using a "waterproof" or "water-resistant" product.

"There is no such thing as waterproof sunscreen, and the FDA has now suggested its removal of the term of sunscreen bottles, no sunscreen is waterproof," Davis said.

Davis notes that protective clothing can also play a key role in blocking harmful rays. "Of course, no sunscreen talk is complete without the mention of broad-rimmed hats and sunglasses."