Dr. Rigel

As the U.S. Food and Drug Administration (FDA) weighs new guidelines that would cap SPF ratings at 50+, experts debate whether the new super sunscreens live up to their hype — or add to consumer confusion.

"There is a difference between a real SPF 100 and a real SPF 50, 30 or 15," says Barbara Gilchrest, M.D., professor of dermatology, Boston University School of Medicine.

Dr. Gilchrest

Alternately, she says it's also essentially accurate that creating a fraction by placing the numeral "1" above the SPF value will indicate how much UVB penetrates a properly applied product. For example, an SPF 100 product would transmit one-one-hundredth, or 1 percent, of the sun's UVB rays.

Dr. Lim

Damage over time

But a researcher for a major pharmaceutical company and sunscreen-maker disputes that.

Yohini Appa, Ph.D., says that when one considers UVB buildup over time, "There is a dramatic difference between SPF 50 and SPF 100."

She is senior director, scientific affairs, Johnson & Johnson, maker of Neutrogena's new Ultra Sheer Dry-Touch Sunblock SPF 100+. If SPF 100 were a Kevlar vest, she says, one of 100 bullets would penetrate, versus two of 100 at SPF 50. "That's twice as much damage with SPF 50."

A recent study provides clinical evidence that higher SPFs provide superior protection, she says. In a split-face study involving 56 ski instructors, investigators randomized 28 participants to apply an SPF 85 sunscreen to one side of their faces once daily, while the other participants used SPF 50.

"Those who used the SPF 85 were basically protected, while eight of the 28 who used SPF 50 had some sunburning (Russak J, Rigel DS. J Am Acad Dermatol. Publication pending)," says study co-author Darrell S. Rigel, M.D., clinical professor of dermatology, New York University.

That's another advantage the higher SPFs have in extreme conditions, he says. "That extra protection will make a difference."

Bench versus beach

Experts also debate how underapplication of sunscreen impacts UV protection. The FDA requires that manufacturers test products at a thickness of 2 mg/cm2, Dr. Rigel explains. But, realistically, "Nobody applies that concentration."

Rather, several studies have shown that people actually apply 20 percent to 50 percent of this amount, he and Dr. Gilchrest say.

When consumers use too little sunscreen, Dr. Gilchrest says, SPF protection decreases exponentially. At half thickness, she says, an SPF 100 product yields approximately SPF 25.

Dr. Appa counters that Neutrogena's research shows that when people underapply sunscreen, the decrease in protection roughly parallels the degree of underapplication.