Sunscreens are an essential part of summer vacations. However, the chemicals contained in some of them may be harmful to the environment and health. Researchers at the University of Maryland are testing a surprising alternative: methylene blue.
The easiest way to protect yourself from the sun’s rays is to stay in the shade or apply sunscreen well before exposure. However, those that limit the harmful effects of the sun’s UVA and UVB rays are a real poison to the marine ecosystems.
The vast majority of sunscreens on the market use oxybenzone and its derivatives, among other molecules, as chemical UV filters. This organic compound, which gives sunscreens their white color, absorbs some of the UVA rays (320-440 nm) that penetrate deep into the skin and cause the oxidative stress responsible for skin aging, as well as the UVB rays (280-320 nm) that cause sunburn and DNA damage. But oxybenzone has gotten a bad press, suspected of being an endocrine disruptor, causing allergies and poisoning marine ecosystems, corals being the most notorious victims.
Researchers at the University of Maryland, are proposing a new and rather unexpected UV filter: Methylene blue, a laboratory dye synthesized in 1876. Due to its strong antioxidant power and molecular structure, scientists wondered if it could act as a chemical UV filter and serve as an alternative to oxybenzone.
Methylene blue absorbs the strongest UV rays
Methylene blue has already been shown to work as a DNA repair agent. The same research team had shown that it activates metabolic pathways that repair DNA damage. To investigate this further, they exposed human keratinocytes, the cells of the skin’s surface layer, to increasing doses of UVB after treatment with methylene blue.
DNA damage and mortality occurred less frequently in the treated cells than in the untreated cells. The scientists compared the filtering properties of methylene blue with those of oxybenzone. Their results showed that methylene blue absorbs a broader spectrum of UV rays, including high-energy UVB and UVC than oxybenzone.
Non-toxic in the experiments
What about the toxicity of methylene blue on corals? To get an idea, scientists compared the health of Xenia umbellata soft coral in the presence of methylene blue or oxybenzone at the same dose (1 µM) for seven days. At the end of the experiment, methylene blue did not change the health of the coral, while pieces of dead tissue were observed in the presence of oxybenzone.
This toxicity test does not allow for definitive conclusions about the non-toxicity of methylene blue. It appears to be harmless in this experiment. Further experiments will be needed to confirm non-toxicity to corals and the marine environment in general.
Mineral UV sunscreens are a more environmentally friendly alternative to chemical filters, but they are more expensive to purchase and leave a white film on the skin. Perhaps tomorrow’s chemical sunscreens will be blue.