Most people reach for sunscreen when the temperature climbs and put the bottle away once it drops. Your skin doesn’t work on that schedule. UV rays reach you every month of the year, and the damage they cause adds up whether you feel the heat or not.

Summer: the obvious season

Summer is when UVB rays, the ones mainly responsible for sunburn, are at their strongest. That burning sting is the short-term signal, but the longer-term problem is what UV does underneath. About 90 percent of nonmelanoma skin cancers and 86 percent of melanomas are linked to UV radiation from the sun. Sunscreen is the daily habit that lowers that exposure.

A few summer basics worth repeating to patients: use a broad-spectrum sunscreen (it covers both UVA and UVB), and reapply every two hours, more often after swimming or sweating. History Facts notes that dermatologists set SPF 30 as the practical minimum.

Winter: the season people skip

This is where the message gets interesting, because cold weather feels like permission to stop. It isn’t.

UVA rays stay constant all year and pass straight through clouds and fog. They also penetrate glass, so a bright day near a window still exposes your skin. If your patient thinks an overcast January afternoon is safe, it isn’t.

Snow makes it worse. Snow and ice reflect up to 80 percent of the sun’s UV rays, so the light hits you twice, once from the sky and once bouncing back up. Add elevation and the numbers climb: UV exposure rises 4 to 5 percent for every 1,000 feet above sea level, which is why a day on the ski slopes is as hard on your skin as a day at the beach. Skiers, snowboarders, and even people watching from the lodge are all in range.

One more detail that surprises people: the face, head, and neck stay exposed year-round, and that’s exactly where most skin cancers show up. A hat and sunglasses aren’t just for July.

Before there was a bottle: how people used to cope

Sun protection is not a modern invention. People were dodging the burn for thousands of years, just with stranger tools.

• By around 3000 BCE, societies were using parasols and umbrellas for shade. In ancient Egypt these were often made from palm leaves or feathers.
• Ancient Greeks applied olive oil to their skin. Modern testing puts its natural SPF at about 8, enough to take the edge off a burn but well short of today’s SPF 30.
• Egyptians used rice bran, which actually absorbs UV light, along with jasmine and lupine in their skin treatments.
• Zinc oxide, still an active ingredient in mineral sunscreens today, was used in India as far back as 500 BCE. In Myanmar, a ground-bark paste called thanaka has been worn for more than 2,000 years.
• The oddest entry: wealthy women in 16th-century France and England wore black velvet “visard” masks to keep their skin pale. Most had no straps, so the wearer held the mask on by biting a bead, which meant she couldn’t talk while wearing it.

The modern version arrived late. During World War II the U.S. military issued a thick red petroleum salve nicknamed “red vet pet.” A Florida pharmacist named Benjamin Green smoothed it out with cocoa butter and coconut oil in 1944, and that formula became Coppertone.

The takeaway

The tools have gotten better. The instinct hasn’t changed. People have always looked for ways to stay covered when the sun is out, and now we have something that works far better than olive oil or a velvet mask. Broad-spectrum SPF 30 or higher, every day, in every season, is the whole message.