The plagues of our modern society include diabetes, allergies, asthma, obesity, autism, and numerous digestive system disorders such as irritable bowel syndrome, colitis, Crohn’s disease, and celiac disease. The symptoms and difficulties inherent with each of these diseases is different. However, modern molecular biology research techniques have revealed a commonality. People with each of these ailments have a microbiome that is strikingly different from that of healthy people. Micro-bio-what? This blog, Mostly Microbes, explores the interactions between microbes and us, their human hosts. In particular, I focus on the importance of the human microbiome for and during pregnancy, birth, infancy, and early childhood. What is the microbiome? The microbiome is all the microbial cells living in a particular location [1]. In the case of humans, the human microbiome includes over 100 trillion bacteria, viruses, and fungi that live in or on your body [2]. Perhaps as much as ten times more microbes make up your body than human cells [2] (though new estimates [3] put the number of human cells at 3.72 trillion instead of 10 trillion). You are their home. You may have immediately thought “ew- I want to wash my hands now!”, but hold on a minute. The