Think sunscreen is enough to protect you from skin cancer? Think again.
Researchers from Yale University have concluded that damage from the sun continues even after we are out of the sun or away from the tanning bed.
UVA radiation causes lesions or DNA damage to melanocytes, which are the skin cells that produce the skin pigment known as melanin.
Melanin is a protective pigment in skin, blocking UV radiation from damaging DNA and potentially causing skin cancer. Melanin does protect us, but this research shows it can also do us harm.
How Melanin Can Hurt Us
Researchers say UV radiation generates reactive oxygen and nitrogen that energizes an electron in melanin.
That energy can cause DNA lesions, which can lead to cancer-causing mutations. The lesions typically appear less than one second after UV radiation exposure.
The researchers noted, however, that particular damage can also take place more than three hours after exposure to UVA radiation, which comes from the sun and from tanning beds.
“You have two opposing things happening at the same time: Melanin protecting you and melanin damaging you,” explained Dr. Doug E. Brash, a skin cancer researcher at the Yale School of Medicine. “You’ve got this race going on between melanin blocking and protecting you.”
Brash said it is a simultaneous event — melanin protects us at the same time sunlight is trying to damage our cells.
“A consequence of these events is that melanin may be carcinogenic as well as protective against cancer,” the new report stated.
“We didn’t see this coming,” Brash added.
Examining Melanin in the Dark
In the study, researchers exposed mouse and human melanocyte cells to UV radiation using a UV lamp. It led to cyclobutane pyrimidine dimers (CPDs), a type of DNA damage.
The melanocytes produced CPDs immediately and continued to do so hours after UV exposure ended. Cells without melanin generated CPDs but only during exposure to UV radiation.
"If you look inside adult skin, melanin does protect against CPDs. It does act as a shield," Brash said in a statement. "But it is doing both good and bad things."
Next, the scientists looked at the damage after sun exposure. They prevented normal DNA repair in mouse skin samples and found that half of the CPDs in melanocytes were created in the dark.
Another researcher learned that the UV light activated two enzymes that came together to “excite” an electron in melanin. That energy, which is dubbed chemiexcitation, was delivered to DNA in the dark. It created the same DNA damage that sunlight caused in daytime.
Protecting Our Skin Inside and Outside
When we put on sunscreen during UV light exposure, it can stop the risk of sun damage.
After we leave the beach or the tanning bed, however, any exposure to UV radiation can still cause this harmful reaction with melanin.
Brash’s team is looking to create a product that could suppress the reaction. It would be like an “evening after” sunscreen. People could apply it like they would a moisturizer when they come in from the sun.
“Hopefully we can come up with a way to intervene,” Brash said.
In the meantime, be careful with UV exposure, Brash warned.
“I think it’s still true that it’s best not to go in the sun between 10 a.m. and 2 p.m.,” he said. “Just be reasonable.”