While science focused on infectious pathogens and environmental bacteria as triggers of the inflammation brake, the microbiome remained an unknown quantity for a long time. Only when the new techniques of high-throughput sequencing of DNA became available from the 2010s onwards did researchers throw themselves into this white spot on the map and analyze the bacterial flora of even the most remote corner of the body. It became clear that the microbiome of the gut, mucous membranes, and skin was another important group of bacteria influencing the immune system. The infectious pathogens and environmental bacteria did not lose their importance, but they did take a back seat for a while; their research is only now being reactivated—rather tentatively. The star, the “new girl in town”, is now the microbiome.