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A season is planned for everything, a time for every experience under the sky … A time to kill and a time to heal, a time to destroy and a time to build. Ecclesiastes 3: 1-3 (The Bible of Israel ™)
Teacher. Carmit Levy from Tel Aviv University. (Credit: TAU)
Nobody can hear the ticking of his brain. But we all have biological clocks in our body that are responsible not only for sleep and wakefulness but also for the release of hormones, body temperature, fertility, aging and others. functions when you are hungry.
Scientists from Tel Aviv University and the Technion-Israel Institute of Technology in Haifa discovered that our tanning also functioned according to the biological clocks of our body.
Researchers learned from their experiments on human skin and mouse samples that a 48-hour cycle synchronized skin protection mechanisms after exposure to ultraviolet light. The research has just been published in the journal Molecular cell, who also dedicated the title page to their work.
"Skin exposure to the sun induces two protection programs – the stress response and the pigmentation – the first in minutes and the second a few hours later," they wrote in the newspaper. Although serving the same physiological purpose, it is unclear if and how these programs are coordinated.
"To our surprise, we found that an exposure every other day rather than a daily exposure causes an optimal tan," said Professor Carmit Levy of the department of Human Genetics and Biochemistry faculty SAU of TAU, who worked with his doctoral student. Hagar Malcov-Brog. "In fact, we showed that the frequency of exposure was very important and we sought an explanation for the phenomenon."
In collaboration with Prof. Shai Shen-Or and doctoral student Ayelet Alpert from the Technion Rappaport Faculty of Medicine and Dr. Mehdi Khaled from France, they identified a process that synchronizes the natural defense mechanisms of the skin.
During the course of evolution, when the precursors of modern humans lost the fur that protected their bodies, our skin developed natural defense mechanisms arising from exposure to the sun's rays, explained Levy. "One of them is the pigmentation mechanism – the tan used commonly – which creates a physical-mechanical protection of the skin. It recruits the immune system to repair the damage to DNA caused by UV rays that can cause skin cancer. "
Many scientists around the world are studying the effect of the sun's rays on the skin, but according to Levy, most of the studies focus on the responses related to the intensity of exposure. Israeli researchers, however, examined the effect of another factor, frequency. To this end, they exposed skin samples to UV radiation at a constant intensity – at sunlight from summer to noon – but at different frequencies, for example every other day, intermittent exposure, and so on.
The researchers examined the skin samples every hour after exposure and collected various data on the response of defense systems to exposure at different frequencies. Among other things, they measured the levels of different proteins in the skin, pigmentation levels, repair of RNA and DNA. They found that proteins expressing certain genes appear in the skin in a clear and well-synchronized sequence within 48 hours of exposure to UV rays.
The team built a mathematical model that showed that the MITF levels (transcription factor inducing melanocytes) Protein – which is responsible for the protective mechanisms of the skin – goes up and down as a wave fades over time. This activates the defense mechanisms simultaneously.
"Imagine that you threw a stone in a lake and formed waves. If you cast another stone before the first wave fades, the wave created by the second stone will disrupt the pattern, "said Shen-Orr. "That's exactly what's happening in the skin. Additional exposure to the sun during the first wave of synchronization reduces the effectiveness of the skin protection system. "
The mathematical model has been verified in a laboratory experiment. "We have discovered that the life cycle of the skin defense mechanisms is 48 hours, unlike the natural sun exposure that occurs every day, that is, every 24 hours Levy concluded. "
The number of skin cancer cases is increasing every year. UV exposure is a major risk factor for all common skin malignancies, they concluded. MITF has been shown to play a key role in the development of melanoma. the deadliest type of human skin cancer.
"We are now trying to understand why this could be related to the expression of vitamin D, related to sun exposure and which reaches its peak every 48 hours. In any case, said Levy, "we all recommend that for optimal protection after sun exposure, let the natural mechanism of your skin finish what needs to be done – and do not expose yourself too often to the rays of the skin. Sun."
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