University of Manchester: Long-Term Sun Exposure May Disrupt the Skin’s Biological Clock

Long-term exposure to sunlight may disrupt the internal biological clock of human skin, according to researchers from University of Manchester, University of Pennsylvania, and No7 Beauty Company. The study was published in the Journal of Investigative Dermatology. Scientists believe that this disruption of circadian rhythms may be one of the reasons behind accelerated skin aging and chronic inflammation.

For the first time, researchers directly compared the function of the “biological clock” in areas of skin that had been exposed to sunlight for decades with areas usually protected from the sun. Skin samples were taken from the forearm and upper buttock of 20 volunteers at different times of day — during the afternoon, evening, night, and early morning. The scientists then analyzed the activity of thousands of genes linked to the body’s circadian rhythms.

The results were unexpected: in skin constantly exposed to ultraviolet radiation, internal rhythms were significantly weaker and shifted in timing. Particularly concerning was the disruption of genes responsible for repairing DNA damage. Under normal conditions, many cellular repair processes become more active at night, when the skin is no longer exposed to sunlight. However, chronic ultraviolet exposure appears to interfere with this delicate synchronization.

Scientists suggest that this may accelerate photoaging — the process in which skin loses elasticity, wrinkles develop, inflammation increases, and tissue damage accumulates. Researchers note that ultraviolet radiation not only damages cells directly but also literally “throws off” the skin’s internal clock.

The authors emphasize that circadian rhythms regulate nearly every aspect of the body, from sleep and body temperature to immunity and metabolism. In recent years, a growing number of studies have linked disruptions of biological clocks to increased risks of dementia, cardiovascular disease, and mental health disorders.

At the same time, the researchers acknowledge the study’s limitations. Only 20 women of European ancestry between the ages of 51 and 63 participated in the research.

The findings have already attracted significant interest from cosmetics manufacturers and dermatologists.

Scientists believe that in the future, skincare may increasingly take the time of day into account — for example, determining when protective or restorative products should be applied for maximum benefit.

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