Visible light is a hidden danger that most commercial sunscreens do not block.

A team at the Center for Research on Redox Processes in Biomedicine (Redoxome)—one of the Research, Innovation and Dissemination Centers (RIDCs) funded by the São Paulo Research Foundation, FAPESP—have developed a new colored sunscreen that could combat the damaging effects of long-wavelength ultraviolet radiation (UVA) and visible light on the cells that produce keratin.

“We knew visible light could damage the skin, but we’ve gained a deeper understanding of the mechanisms by showing that UVA stimulates accumulation of a pigment called lipofuscin, which later acts as a photosensitizer to visible light in the epidermis,” Maurício Baptista, a professor at the University of São Paulo’s Chemistry Institute (IQ-USP), in Brazil and a member of Redoxome, said in a statement. “Basically, UVA damages the skin, and visible light augments the damage.”

Despite the rising consumption of sunscreens, skin cancer cases continue to increase.

Baptista explained how a colored sunscreen could help block the impacts of visible light, which accounts for 45 percent of the solar radiation that reaches the skin.

“A colored sunscreen shouldn’t be just any color,” he said. “It should be the same hue as the individual’s own skin tone.

“We’ve developed a product that protects the skin against UVA, UVB and visible light,” he added. “It uses nanoparticles coated with a fine film of melanin.”

UVA radiation penetrates deeper into the epidermis and causes damage that is perceptible in the long run.

“We believe the types of skin cancer characterized by exposure to UVA must also be due in large measure to the action of visible light, which has never been taken into account,” Baptista said. “UVA and visible light cause similar lesions.

“They act together,” he added. “Both the oxidative damage done by UVA and the effect of visible light cause DNA oxidation.”

This is different from how shortwave ultraviolet (UVB) damages the skin, which is directly absorbed by epidermal cell DNA.

The response is much faster, consisting initially of redness for people who produce less melanin, and the skin is more severely damaged, while infrared radiation heats the blood vessels and causes inflammation.

The researchers analyzed how keratinocytes are damaged by visible light, building on a 2014 study where the researchers focused on finding how melanocytes respond to visible light.

The researchers found that the keratinocytes are the first victims of the damage done by UVA, which makes the cells produce lipofuscin that acts as a visible light photosensitizer, generating reactive oxygen species and mediating light-induced damage.

 

Baptista stressed the importance of people protecting themselves from all types of light.

“It would be quite wrong to interpret the study as saying we don’t need to use sunscreen,” he said. “That’s not the point at all.

“UVB is far more toxic than UVA and visible light, but the number of cases of severe skin cancer is rising largely because people have been protecting themselves from UVB for at least 40 years, yet for a long time, there were no products to block UVA,” he added. “There aren’t any visible light blockers even now.”

The study was published in the Journal of Investigative Dermatology.