After a brutally cold winter, it feels good to get outside and soak up the sun.

That feeling of well-being that you get on a sunny day is not imaginary. Sunlight can improve your mood, regulate your biological clock and help your body manufacture vitamin D.

But the sun can also be your enemy. It can cause your skin to thicken, darken and wrinkle. It can trigger deadly skin cancers. It can even rob you of your vision.

This doesn’t mean you have to stay sequestered indoors. But doctors say if you do venture out into the sun, be sure to take precautions.

“No one ever uses enough sunscreen,” said Dr. Gabrielle Sabini, a dermatologist at North Atlanta Dermatology in Duluth. “They don’t realize that a single application should consist of at least enough lotion to fill a shot glass. It should be applied very liberally.”

It’s also important to pick the right type of sunscreen. Sabini recommends an SPF (sun protection factor) higher than 15. The SPF is a measure of how long the product allows you to stay in the sun before your skin begins burning.

Most people need an SPF of at least 30. But Sabini said the number shown on the bottle doesn’t necessarily indicate how well the product will work for you.

“The number is based on tests where people covered all of their exposed skin (with the sunscreen),” she said. “If you don’t use the same amount used in the studies, you’re not going to be getting the full SPF.”

But the SPF rating only measures protection against UVB radiation. Sunlight contains two major types of harmful ultraviolet radiation, UVA and UVB. Each affects the human body differently.

“UVA rays are the ones found in tanning beds,” said Sabini. “They don’t burn, but they’re associated with melanoma (the most lethal skin cancer), wrinkling and brown spots. UVB rays cause sunburn, as well as squamous cell and basal cell carcinomas (less serious cancers that form in the upper layers of the skin).”

And the skin isn’t the only part of the body that’s at risk.

“UVB rays can damage the tissues of the eye,” said Dr. Jack Chapman, a Gainesville ophthalmologist. “It can contribute to macular degeneration (a major cause of blindness) and
formation of cataracts.”

Chapman recommends buying sunglasses that specifically protect against UVB rays.

OK, so you’re wearing your sunglasses and maybe even a broad-brimmed hat. You’ve slathered sunscreen on every inch of exposed skin. Are you completely safe from the sun?

Not quite. Sabini said most people don’t know that UVA rays go right through clothing.

“You can get sun damage under your shirt, even though you don’t burn,” she said.

The UVA rays can cause cells in the lower layers of the skin to mutate, triggering the growth of melanoma.

To prevent this, Sabini said, you can either wear more than one shirt or wear a single shirt with fabric so tightly woven that sunlight can’t pass through.

“I recommend sunscreen clothing, if you can find it,” she said.

There is a significant downside, however, to blocking out the sun. Your body needs sunlight to make vitamin D, and most Americans are already deficient in this vital nutrient.

Sabini said that’s not a good reason to skip the sunscreen. “Even with the vitamin D (deficiency) epidemic going on, dermatologists have not changed their recommendations,” she said. “Keep covered up, and have your vitamin D level checked. If it’s low, you can take supplements.”

Sabini believes a lack of vitamin D isn’t nearly as dangerous as melanoma, which kills about 8,500 people in the United States every year.

And even though melanoma often appears on parts of the body that aren’t typically exposed to the sun, “research shows that people who spend a lot of time in the sun are much more likely to get melanoma.”

Dark-skinned people often believe that because they don’t sunburn easily, they don’t need to use sunscreen. But Sabini reminds them that it’s the non-burning UVA rays that increase the risk of melanoma.

“Everyone should wear a sunscreen that blocks both UVB and UVA,” she said. “It doesn’t matter whether you’re black, Hispanic or Asian. Melanoma is a really scary disease, and it kills people.”