Years of chronic exposure of human skin to sunlight strongly disrupts its body‑clock rhythm, according to a pioneering study led by University of Manchester, No7 Beauty Company, a member of The Boots Group, and University of Pennsylvania scientists.
The findings could explain how ultraviolet (UV) light triggers inflammation and damage in exposed skin, so-called photoageing, which breaks down its supportive structure, altering how its cells behave.
Published in the Journal of Investigative Dermatology, the study could have important implications on skin health and the design of skincare products that takes into account the time of day when they are applied.
The study is the first to directly compare daily rhythms of genes being turned on and off in human skin exposed to and protected from sunlight over half a century.
Almost all organs – including skin – exhibit 24 hourly rhythms which allows the body to anticipate and adapt to changes associated with the light-dark cycle, including daily exposure to solar radiation.
Lead researcher Professor Qing-Jun Meng from The University of Manchester said: “According to the “escape from light” hypothesis, one of the driving forces of the evolution of clocks in ancient life forms was to restrict vulnerable biological processes – specifically DNA synthesis and cell division – to the nighttime to avoid harmful radiation from the sun.
“So over evolution, organisms that timed DNA copying to happen at night or in low-light conditions had fewer mutations and survived better. Their built-in “clocks” helped schedule risky processes for safer times. This ancestral protective mechanism seems to be still evident today in mammalian organs, such as the skin.
“Understanding human skin chronobiology and how it adapts to and anticipates daily variations in stressors such as UV light is critical for the maintenance of skin health.”
He added: “To the best of our knowledge, this is the first in vivo skin body clock study that directly compares UV damaged against sun protected skin from the same human subjects.
“And we found chronic UV light exposure is linked to weaker body clocks, and earlier rhythms, suggesting that our skin body clocks could be disrupted or reprogrammed, which could have important implications on skin health.”
The researchers worked with 20 volunteers by taking skin biopsies from both the covered upper buttock and exposed dorsal forearm at noon, 6PM, midnight, and 6AM, across a 24-hour cycle.
Both sets of samples were taken from the same people, ensuring the results were more statistically reliable.
Gene activity in the samples was measured using RNA sequencing, and sophisticated statistical analysis identified how strong the body clock cycles were and when each gene’s activity peaked.
“The University of Manchester is a public research university in Manchester, England. The main campus is south of Manchester City Centre on Oxford Road.”
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