[noun] Free radicals are oxidising molecules that are generated by various external factors, such as exposure to UV rays (leading cause), stress, pollution, blue light from screens or smoking tobacco. Oxidation, generated by free radicals, is not a problem as long as the latter are not too abundant. If they multiply, the cells are saturated with oxygen. This oxidative stress causes signs of premature skin ageing to appear: loss of skin elasticity and formation of wrinkles.