Cold and flu occur when the body comes into contact with something it hasn’t experienced before. While you are lying on the couch with a box of tissues by your side, behind the scenes your body is hard at work trying to figure out what this strange new element is and how to conquer it, throwing antibodies at the unwanted object to see which will kill it best. The victorious antibody is then handed off to a memory cell in preparation for the next invasion. T-cells—a kind of white blood cell that roams the body in search of external invaders—are deployed to kill off any remaining hint of the intruder, and other cells follow to clean up the damage. Ideally, if the immune system were working perfectly, we would never experience cold or flu symptoms, because any internal threat from a microorganism would be dealt with so efficiently that we’d never know it happened.

Immunity begins to develop as soon as we’re born. With every new substance your infant self encounters, new organisms are introduced to your body. New parents often want to protect their infants and maintain extra-cleanliness for their little ones, but we’re finding more and more evidence that sterile, antibacterial environments are actually terrible for the immune systems of children and adults alike. When a baby starts crawling and really exploring his environment, picking up whatever ends up in his hands and sticking it in his mouth, parents freak out—but that baby’s doing the best possible thing for himself. These tiny samples of bacteria, viruses, fungi, and microorganisms find their way from a baby’s curious mouth into his developing gut. Here, helpful bacteria will grow and flourish, while the newborn baby body learns how to strengthen itself to combat dangerous “bugs.” By the time a child reaches adulthood, assuming he’s had the chance to develop a robust immunity, colds and flus should be rare.