“Eat dirt!” is a phrase I remember well. It was in the title of an article published by Harvard University environmental health professor, Dr. Scott T. Weiss, and it captured my attention while I was learning about an immunological concept known as the “hygiene hypothesis.” The core of the idea is that we live in a microbial world: an environment full of bacteria, parasites, viruses, and fungi. And that our interactions with these microbes after birth are extremely important to educate our immune systems to function properly. When we are born, our immune systems are still maturing. I like the way researchers led by microbiologist Sally F. Bloomfield expressed it in their study: “The immune system is a learning device, and at birth it resembles a computer with hardware and software but little data. Additional data must be supplied during the first years of life, through contact with micro-organisms from other humans and …