A huge number of microbes live in and on us. They’re in our lungs, mouths and intestines, and on our skin. Scientists know they help us digest, breaking down what we eat, but they are discovering that each individual’s microbiome, the collection of microbes in their body, helps protect them. For example, bacteria in the nose produce antibiotics that attack viruses we breathe in. They have also been found to cure infections in the digestive tract and elsewhere and to help the immune system. Yet researchers still don’t know exactly how microbes operate on our health, or why studies disclose that diseases are often associated with major changes in our bacterial ecosystems. For example, people who suffer from asthma have a different set of microbes from people without the condition. And obese people have species not found in normal-weight people. So scientists are investigating the huge number of microbes in our bodies and their DNA to find out more about how they help keep us healthy. That knowledge will help discover how the microbiome can be used to fight disease. Read Carl Zimmer’s article How Microbes Defend and Define Us for more details.