In 1903, physician Niels Ryberg Finsen received the third Nobel Prize awarded in physiology or medicine for demonstrating that exposure to the sun’s ultraviolet (UV) rays cured patients suffering from skin infections of tuberculosis. Not only does UV directly damage bacterial DNA, but a family of bacterial molecules known as porphyrins can form toxic reactive oxygen species when exposed to UV and near-UV radiation, effectively turning them into bactericidal agents. UV and other wavelengths of light have also commonly been used to treat acne, another skin condition caused by bacteria, as well as genetic and autoimmune skin disorders such as psoriasis and loss of pigmentation (vitiligo).