How the Sun Changes Your Skin

A sunburn or tan is the obvious result of skin exposure to sun, but how exactly does the sun cause less visible changes to our skin?

Long hours of summer sunshine may improve our moods and provide ample opportunity for sunbathing, but what exactly does soaking in those rays do to our skin?

"What happens when the UV light hits our skin is the energy penetrates our skin and hits our DNA," dermatological surgeon Jerry Brewer of the Mayo Clinic said. "One of the most common things that happens after that is the formation of a pyrimidine dimer. That's when two different building blocks of DNA that are next to each other form a bond connecting them more tightly than they should be.

"So when our body is replicating that DNA, it's hard to figure out what that is. Instead of seeing two building blocks, it sometimes sees it as only one. And that causes a frame shift mutation."

Most of the time, Brewer said, the body is good about detecting those frame shifts, and it even has a repair system that uses the mirror image DNA strand to fix the broken one. But every once in a while, the repair system fails.

Still, there's a backup system in which cells commit suicide if it's changed too much. But when a cell slips by those two systems, "it sometimes gets changed in a very dramatic way that can lead to a lot of things, including cancer."

Ironically, sunlight can also synthesize vitamin D, which is not only essential for bone growth and absorbing calcium, but can help prevent DNA damage (which shows up as a tan or a sunburn) by reducing oxidative stress, Brewer said.

It can also help regulate the growth of cells, important to the prevention of cancer. When the light hits your skin, a gene known as POMC (pro-opiomelanocortin) gets activated, which leads to increased melanin and increased beta endorphin.

"That's almost like a drug; it can give a person an internal high, and that's why some people can become addicted to tanning," Brewer said.

It's no excuse to lay out your beach blanket, though: it only takes a few minutes to absorb plenty of vitamin D, depending on your complexion. Darker skin can tolerate more time, whereas a light-skinned person would get plenty of exposure even wearing long sleeves and pants.

And slathering on the sunscreen isn't a cure-all: Epidemiological data has pointed at UV light as a source of melanoma. New experimental research published in the journal Nature confirms both that it does and that sunscreen does not provide complete protection. The experiments on mice also pinpointed the exact gene that UV light mutates: Trp53.

So where's the balance?

"The bottom line is, DNA damage is bad, vitamin D is good. It's best to reduce DNA damage by reducing UV exposure, and keep vitamin D levels up through diet," Brewer said.

UVB radiation (from sunlight) triggers an enzyme to start the process of increasing melanin, which is synthesized inside cells called melanocytes. Once made, the melanin leaves the cell and darkens the color of your skin.

"We're not trying to ruin it for everybody; people do want to go out and be in the sun," said Richard Marais, author of the Nature study and director of Cancer Research U.K.'s Paterson Institute for Cancer Research.

"But we need to start to understand that it's a more complex message -- slapping sunscreen on doesn't mean you're good to go for the day. You need to combine it with other sun protection, such as loose-fitting clothes, sunglasses, and staying out of the sun when it's at its hottest point."

Also, individual skin varies widely, and sun protection may take different forms from person to person, Marais said.

DNA damage to the skin shows up as sunburn or tan.

April 22, 2011 --

Earth Day isn't just about life on land. It's also an opportunity to explore the organisms that inhabit the oceans. The University of Miami's Rosenstiel of Marine and Atmospheric Science hosts an annual photo contest for the best snapshot of life under the sea. More than 600 images were submitted from an international pool of photographers. This shot of two transparent gobies, taken in MarsaAlam, Egypt, claimed the top prize as the best overall photo of the competition. Explore some of the other photos to claim top prizes in the 2011 underwater photography contest in this slide show.

PLANET GREEN: The Most Stunning Bodies of Water in the World

This pygmy seahorse, Hippocampus bargibanti, may be difficult to spot, given how well it blends into its environment and the fact that these seahorses don't grow any larger than an inch. But this snapshot earned first prize in the contest's "Marco" category.

This vibrantly colored nudibranch (Cratena peregrina) was seen in Tarragona, Catalonia, Spain.

A nudibranch and a mantis shrimp rest on the sea floor of Bali's Seraya Beach in Indonesia.

Cuttlefish are seen mating off in the Oosterschelde estuary near the town of Zeeland, Netherlands. This photo took the top prize in the "Wide-Angle" category.

A stingray is surround by cardinal fish in this photo taken in Mogan in Gran Canaria, Spain.

A school of barracuda gathers in the Sudanese Red Sea.

This brightly colored jellyfish was spotted in Lake Worth Lagoon in Riviera Beach, Fla. The photo took the top prize in the "Fish or Marine Animal Portrait" category.

This web burrfish (Chilomycterus antillarum was spotted in the same location as the jellyfish in the previous slide. If it looks like it's smiling, that's because this photo took home second prize in the portrait category.

This frog catches its own reflection at the surface of a lake in Belgium just as the photographer snaps a picture.

This snapshot of an orange spotted filefish, Oxymonacanthus longirostris, claimed the top prize in the "Student" category. The fish was spotted in the water of YasawasIslands, Fiji.

This whale shark (Rhincodon typus) and its entourage were spotted cruising the depths of Ningaloo Reef, Western Australia.

If you look closely at this photo, you'll see a blue striped cleaner wrasse attending to the much more prominent Emperor Angelfish in in the foreground.