It’s a message we’ve all heard before: Put on sunscreen before spending time in the sun. Now a new study suggests people should break out the SPF even on days they don’t necessarily plan to be outdoors for extended periods of time.

The study, published in the Archives of Dermatology (Vol. 139, No. 4: 451-455), found that applying sunscreen every day can reduce the formation of actinic keratoses (also called solar keratoses), a potential precursor to skin cancer.

Actinic keratoses (AKs) are small, scaly patches that can develop on skin that has been exposed to the sun – most frequently on the face, ears, backs of the hands, and arms. They tend to develop in people middle-aged and older, although younger people who live in sunny climates can also get them. Fair-skinned people who burn easily are most at risk.

These lesions are very common, and usually do not cause any symptoms. Sometimes, however, they can develop into squamous cell cancer.

Researcher Steven Darlington, BSc, and colleagues at the Comprehensive Cancer Research Center of Queensland Institute of Medical Research in Australia, wanted to determine if regular application of sunscreen could reduce the formation of actinic keratoses – and thus potentially reduce the formation of skin cancers.

For their study, they recruited more than 1,600 adults age 25-74 from the town of Nambour, Australia, a subtropical area with intense sun exposure. All the participants were examined for AKs at the beginning of the study in 1992. Half the people were assigned to apply an SPF 16 sunscreen to their head (face and any exposed scalp), neck, arms, and hands every morning; the rest were told to apply sunscreen as they normally would.

Two years later, in 1994, the researchers checked the participants for AKs again. Though participants in both groups had developed new AKs over that time period, people who had been assigned to use sunscreen daily had developed 24% fewer than people who used sunscreen at their own discretion. The results support previous studies that also indicated sunscreens were effective at reducing actinic keratoses.

And they reinforce the message that sunscreen is important, even if you don’t plan to stay in the sun for very long, said Martin Weinstock, MD, PhD, professor of dermatology at Brown University. After all, a quick walk to the car can unexpectedly turn into 30 minutes of unprotected exposure if you stop to chat with a neighbor along the way.

It’s very easy to get more sun exposure than expected, particularly in areas where the sun is intense, Weinstock explained. “Spring is a key time, because it’s not that hot and people aren’t aware how intense the sun is.”

Weinstock said the findings reinforce the American Cancer Society’s “Slip! Slop! Slap!” message. This skin cancer awareness campaign urges people to slip on a shirt, slop on some sunscreen, and slap on a hat before spending time in the sun.

But it’s not enough to just use sunscreen, Weinstock said. It has to be used correctly.

“You have to put it on before you go out, you have to put on enough of it, you have to reapply it while you’re out, and you have to be sure not to wipe it off,” he said.

Many people forget to reapply, Weinstock says. He recommends putting on sunscreen before going out into the sun, and then again 20 minutes later to be sure to get uniform coverage.