Helicobacter pylori (yellow), a common bacterium that lives in the stomach lining, increases the risk of stomach cancer (brown cells) and peptic ulcers. But over time H. pylori can reduce stomach acid and acid reflux, which may help fend off esophageal cancer. The microbe also appears to help protect us from allergies and asthma. Some scientists suspect that the dramatic increase in those conditions in the industrialized world could be related to the decreasing frequency of H. pylori in our stomachs, which is partly due to high doses of antibiotics in childhood.
Photograph by Martin Oeggerli, with support from School of Life Sciences, FHNW