It’s long been known that a higher sunblock SPF doesn’t mean you’re completely protected from the sun’s harmful ultraviolet (UV) A and B rays that can cause skin cancer and damage DNA.

Complete protection consists of a mix of factors, including the time of day and not staying out in the sun for too long. A sunscreen is just one tool to help protect the skin from sun damage, said Nneka Leiba, director of healthy living science at the Environmental Working Group (EWG).

Leiba pointed out that hats, clothing and avoiding the mid-day sun are also key to better protecting your sksin from the sun’s dangers.

“Skin cancers are on the rise, so it’s really important to take a holistic look at our relationship with the sun,” she said.

But some sunscreen protection is better than no sunscreen protection at all. Which leads us to the obvious question: What SPF (sun protection factor) is optimal to ward off the most harmful effects of UVA and UVB rays?

But first, we’ve got to remember the SPF value only gives an indication of how the product performs against UVB rays, which causes the most skin cancers and also triggers sunburn.

Seriously wanting to protect oneself from the sun’s rays means protection from both UVA and UVB rays because both of them are associated with skin cancer and skin damage, said Leiba.

For best results, Leiba recommends a sunscreen with an SPF between 30 and 50. At this level, protection against both UVA and UVB rays tends to be more balanced.

“And often with the high SPF products, it’s hard to maintain a good balance,” she said.

Based in Washington D.C., EWG is an activist group that burst into America’s consciousness in 2008 when it first published an analysis of over 900 sunscreens. Its controversial report concluded only 15 percent of sunscreens met its criteria for safety and effectiveness.

Selecting a sunscreen with a mid-level SPF is one recommendation in EWG’s 13th annual Guide to Safer Sunscreens.

A sunscreen rated SPF 15 protects against 93 percent of UVB rays, SPF 30 protects against 97 percent while SPF 50 protects against 98 percent of UVB rays.

But there’s a problem with people believing a high SPF number is safer than a low SPF: they tend to stay out in the sun much longer than they should. These people also tend reapply sunscreen much less often. Taken together, these missteps lead to prolonged sun exposure, thereby increasing the risk for skin damage.

EWG’s Guide to Safer Sunscreens also revealed that sunscreens with mineral-active ingredients such as zinc oxide and titanium dioxide are the “best bets” for both safety and efficacy.

EWG said non-mineral sunscreens use chemicals to block UV rays, and it’s found links between some of these chemicals, such as oxybenzone, and undesirable health outcomes. EWG also recommend against using vitamin A in sunscreens because when applied to sun-exposed skin, vitamin A might speed up the development of skin lesions.

Skin received adequate protection from UV rays when participants applied sunscreen at a thickness of 2mg per cm2. Jean Beaufort/PublicDomainPictures