研究：防晒霜能延缓皮肤老化

最近发表在美国《内科学年鉴》上的一份研究报告指出，每天使用防晒霜可延缓皮肤因光照老化的进程，同时降低患皮肤癌的风险。研究人员将903名年龄在55岁以下的被试者随机分成四组，其中两组每天使用防晒霜，但有一组还会服用β胡萝卜素；另外两组只是在被试者认为有必要的时候才使用防晒霜，也有一组服用β胡萝卜素。研究人员对被试者追踪研究四年半以后发现，每天使用防晒霜的两组被试者皮肤光老化的程度比偶尔使用防晒霜的被试者轻24%，而且各年龄段均无差别。研究人员还指出，一向被认为有抗衰老功能的β胡萝卜素在研究中没有表现出明显功效。

皮肤美容学家建议，早晨出门前要在脸、颈、手等直接被太阳照到的地方涂防晒霜，并且过段时间后要记得重新涂抹；就算一整天都待在室内，也应该使用防晒霜。另外，在使用防晒霜的同时，也要采取其他防晒措施，比如穿长袖衣服、戴宽檐帽、避免在上午十点到下午2点太阳光最强烈的时段出门等。

A new study has found that applying sunscreen every day can do more than lower your risk of skin cancer — it can also drastically reduce the effects of photoaging, or the way frequent sun exposure can make your skin look older. And there's more good news: Even if you slacked off on sunscreen in your youth, middle age isn't too late to benefit from slathering it on.

"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," Dr. Adele Green, a professor at the Queensland Institute of Medical Research at the University of Queensland in Australia, said. "We now know that protecting yourself from skin cancer by using sunscreen has the added bonus of keeping you looking young."

The study, published this week in the Annals of Internal Medicine, also looked at whether taking beta-carotene supplements could have an anti-aging effect. Beta-carotene is a type of antioxidant known as a carotenoid, and has been linked to a reduced risk of skin cancer.

For the randomized-controlled trial, the researchers assigned 903 participants to one of four groups: Those who used broad-spectrum sunscreens daily and take 30 milligrams of beta-carotene, those who used daily sunscreen and took a placebo, those who took the beta-carotene but only used sunscreen periodically, and those who used sunscreen periodically and took a placebo. (All participants were age 55 or younger; the researchers decided it would not be ethical to have a group in which participants used no sunscreen at all.)

The two daily sunscreen groups used UVA/UVB blocking products with a SPF (sun protection factor) of 15 or higher; they applied the product to their head, neck, arms, and hands each morning after bathing, and reapplied it every few hours. The other two groups applied sunscreen where and when they thought they needed it.

The researchers tracked participants for four and a half years, and used putty-like skin molds to document fine lines and wrinkles. They found that the groups using sunscreen every day showed 24 percent less skin photoaging than those who only applied it periodically. The results were the same regardless of age, so even the middle-aged participants benefited from regular sunscreen use.

"The cost-effectiveness of promoting daily sunscreen use based on skin cancer prevention alone is probably substantially higher after accounting for the additional prevention of skin photoaging," wrote the researchers in their report.

Taking beta-carotene had no overall effect on skin aging, the researchers added.

In 2017, the U.S. Food and Drug Administration decided that sunscreen makers could state on the labels that their products reduced the risk of skin cancer and skin aging if used as directed, as long they also advised people to take other precautions, like reapplying sunscreen at least every two hours (more often if you're sweating or swimming), avoiding going out when the sun is most intense (usually between 10 a.m. and 2 p.m.), and wearing long-sleeved shirts, pants, and broad-brimmed hats to shield the skin when possible.

If you only have a few minutes in the morning, it makes sense to apply sunscreen to the areas most likely to see the sun — your face, neck, and hands. All types of sunscreen, even "sport" or "waterproof" formulas, need to be reapplied regularly, and you should wear sunscreen even if you spend all day driving or working indoors, advises Dr. Jaliman, the cosmetic dermatologist.