A new study from Australia provides the strongest evidence yet that regular sunscreen use helps keep skin looking younger.

While dermatologists have long believed sunscreen fights wrinkling, the study in the Annals of Internal Medicine is the first to demonstrate it in a years-long human trial.

“It’s a very important study,” says Henry Lim, a dermatologist at Henry Ford Hospital in Detroit and member of the American Academy of Dermatology.

The study of 903 adults younger than 55 found that after 4.5 years, those assigned to slather on sunscreen at least once a day saw 24 percent less skin aging – at least on the back of their hands – than those left to follow any sunscreen habits they liked.

Researchers who looked for wrinkles and other texture changes on molds made from the skin of the regular sunscreen users saw no significant changes: They gave them, on average, the same grade, on a 0-6 scale, at the end of the study as at the beginning.

The study does not show sunscreen would have the same effects in people older than 55, whose skin changes more rapidly because of the effects of aging itself. Participants in the study had an average age of 39.

Until now, the best evidence that sunscreen prevents so-called photoaging – the visible signs of aging caused by the sun’s ultraviolet rays – came from studies in hairless mice. But human studies have shown that ultra-violent light damages collagen and other fibers that keep skin smooth and taut. Broad-spectrum sunscreens protect against those rays. The new study used a broad-spectrum sunscreen with an SPF (sun protection factor) of 15.

“It is fair to say it was a general assumption that sunscreen would have this effect on photoaging, but our findings now provide the evidence,” says lead researcher Adele Green of the Queensland Institute of Medical Research, who answered questions by email.

The new study also looked at the theory that supplements of beta carotene might slow skin aging, but found no differences between participants who did or did not take them. It’s possible a larger study might find some benefit or harm, Green says.

Lim says the sunscreen findings are especially convincing because the study was done in Nambour, a sunny Australian city that is the same distance from the equator as Fort Lauderdale, Fla. Previous research done by Green’s group in that region has shown sunscreen can protect against skin cancer.

But experts suspect the new evidence about aging may get more attention and change more habits.

“It has been a source of frustration for us that for some sections of the community, the sun-safe message does not seem to be getting through,” Green says. “We now know that protecting yourself from skin cancer by using sunscreen has the added bonus of keeping you looking young.”

That could be a powerful message, says Deborah Sarnoff, a New York City dermatologist and a senior vice president at the Skin Cancer Foundation, a nonprofit group that receives funding from sunscreen makers. “Maybe sheer vanity will encourage young people to be proactive and use their sunscreen, because the cancer fear doesn’t seem to be getting through to them.”

The new study is “very well done,” Sarnoff says, but may underestimate the effect of sunscreen for young and middle-aged adults because it used SPF 15 – which dermatologists consider a minimum – and was conducted in the 1990s, when broad-spectrum formulas were less sophisticated. But she says it’s also possible some of the effect attributed to sunscreen in the study would be seen with the daily application of any moisturizing cream.

A long-term study to test that theory is unlikely to be done: The Australian researchers decided it would be unethical to assign any participants to non-sunscreen products because of evidence that sunscreen helps prevent skin cancer.

Under labeling rules that went into effect in 2012, the U.S. Food and Drug Administration already allows sunscreen makers to say their products can reduce the risk of skin cancer and early skin aging if used as directed, in combination with other measures – limiting time in the sun, especially at midday, and wearing long sleeves, pants, broad-brimmed hats and sunglasses.

The new findings don’t make those other steps any less important, Lim says: “It has to be a total package.”

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