Scientists at Tel Aviv University have discovered a biological mechanism known as the “UV-protection timer,” that protects the skin after it is exposed to the sun over a 48-hour period.“We have identified a mechanism that spreads like a wave through the skin over 48 hours after an initial exposure to ultraviolet rays. This process synchronizes the natural defense mechanisms in the skin,” said Prof. Carmit Levy of the Department of Human Genetics and Biochemistry at TAU’s Sackler Faculty of Medicine, who led the research with doctoral student Hagar Malcov-Brog. “We concluded that exposure to the sun at a frequency of once every two days leads to optimal protection from sun damage.” “The frequency of the wave is 48 hours,” said Prof. Shen-Orr of the Technion-Israel Institute of Technology and Prof. Mehdi Khaled of Université Paris-Saclay, who conducted the research in collaboration with researchers from Tel Aviv. “Imagine you tossed a stone into a pond and saw the ripples spread. Then, before they settled down, you threw in another stone, interrupting the process.”“Similarly, a process of building and breaking takes place in our skin when it is exposed to the sun,” Prof. Levy continued. “Most experts recommend going to the gym every other day, not daily. The same is true of protecting our skin from sun damage. If you interrupt the protection process by sitting in the sun two days in a row, you damage a mechanism that requires a 48-hour process to complete its cycle.”There are two defense mechanisms which protect the skin from damage from UV rays. The first harnesses the immune system, DNA repair, and skin inflammation in order to heal damage and burns from UV rays, while the second is tanning or pigmentation, which provides a physical barrier to protect the skin from further damage.Currently, the researchers are looking to understand how the “UV-protection timer” works, hypothesizing that it may be related to Vitamin D levels.