Top dermatologists agree. "I've been talking about this now for many years, and I know this to be true," Dr. Debra Jaliman, a cosmetic dermatologist and the author of "Skin Rules: Trade Secrets From a Top New York Dermatologist," told Yahoo! Shine in a phone interview. "I can't say I've done a study, but I known this for many many reasons, and I've worked on skin for so many years."
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. Bete-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 2012, 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.
"Let's say they walk to work and they're only outside for 15 minutes, or they take the subway and they're only outside for 5 minutes," Dr. Jaliman told Yahoo! Shine. "Sun damage is cumulative. That 5 minutes or 15 minutes, it adds up over a lifetime."
Even indoors, UVA rays come in through the windows along with the sunlight, she pointed out.
"Just put sunscreen on every morning like you brush your teeth and don't think about it," Dr. Jaliman told Yahoo! Shine. "It takes 30 seconds. Literally, I've timed it."