A few weeks ago The Economist made antibiotic resistance its cover story, and for good reason. We live in a bacterial world. The average person hosts about 39 trillion bacteria. Lucky for us, most bacteria are benign – they crowd out pathogenic bacteria like e. coli in our gut, staph on our skin, and strep in our mouth. Even pathogenic bacteria usually do us no harm unless they invade our bloodstream or otherwise find their way into parts of our bodies that our immune system is poorly equipped to deal with. Some bacteria even confer benefits by priming our immune system to distinguish friend from foe during crucial stages of our early childhood development. For this reason, altering our children’s microbiome by giving them antibiotics every time they have a cold can make them more susceptible to a host of disorders ranging from allergies to autoimmune diseases.