Human visitors can also unknowingly introduce marauding bacteria and fungi. In ancient caves, tourists can carry in skin flakes, cloth fibers, and other materials microbes like to dine on. Having people around also changes the humidity and other ambient conditions, making it easier for pests to grow. This is what happened in Lascaux, where fungi devastated some of the oldest cave paintings in the world. Even the lights installed to help tourists navigate historic caverns encourage microbes to grow, Cesario Saiz-Jimenez, another member of the Environmental Microbiology and Cultural Heritage research group, said in an email.