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Research: Low-frequency exposure to UV frequency causes higher pigmentation of the skin

Professor Carmit Levi

Scientists at Tel Aviv University, led by Professor Carmit Levi and PhD candidate Hagar Malkov of the Human Molecular Genetics and Biochemistry Department of the Medical Faculty, have identified a process that synchronizes various natural defense mechanisms in the skin. The process occurs in a wave over the course of 48 hours following exposure to ultraviolet light. The researchers found that exposure to direct sunlight once every two days results in optimal defense and tanning.

“Just as people are told not to go to the gym every day,” explains Prof. Levi, “the same holds true of exposing the skin to the sun. Continuous exposure prevents the skin from building itself up properly.”

Also participating in the study were Prof. Shai Shen-Or and PhD candidate Ayelet Alpert of the Rappaport Medical Faculty at the Technion and Dr. Madi Khaled of Gustavo-Rossi in France.

“Over the course of human evolution, as humans lost their protective fur, our skin developed other natural defenses that are activated by exposure to sun,” continued Levi. “One of them is pigmentation, or tanning, which produces a physical/mechanical protection for the skin. Another mechanism enlists the immune system to repair DNA damage wrought by UV rays, which might result in skin cancer. These two mechanisms are interrelated and are synchronized in an orderly fashion – interrupting that order by further exposure to the sun compromises the protection".

Scientists around the world have long studied the effect of UV rays on the skin, but according to Levi, most of the research focuses on the body’s responses to the intensity of exposure. The Tel Aviv researchers, o the other hand, investigated the impact of a different factor: frequency of exposure. They exposed skin samples to fixed-intensity UV rays comparable to a summer noontime, but with varying frequencies: daily, every two days, et al.

“We were surprised to discover that exposure every two days, not daily, results in optimal tanning,” noted Levi. “In practical terms we showed that the frequency of exposure is a significant factor, and we looked for an explanation of the phenomenon".

Researchers in Prof. Levi’s laboratory sampled skin each hour after exposure and collected data on the skin’s protective response to the various frequencies of exposure. The measured various protein levels, pigmentation, RNA, and DNA repair. The scientists discovered that proteins produced by certain genes appear in the skin according to a consistent order and synchronization for 48 hours following exposure to UV.

Using this research, the scientists developed materials that can manipulate responses to UV light. “We looked for all sorts of molecules, such as EF inhibitors; we applied them to skin; and we saw the skin get tanned,” explained Levi. “That means a time will come when we can tan skin artificially, but really, by triggering the pigmentation production system naturally, without sunlight, which will protect the skin.”


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