As every parent knows, kids spend their early years exploring the world with their mouths, gumming every germ-riddled object within reach and sampling their ever-sticky fingers. If left to their own devices, it seems likely they would taste-test door knobs and lick the floors of public bathrooms.
However horrifying, their slobbery ways have an upside—building up immune defenses. Their daily buffet of germs provides their immune systems with thorough intel on countless microscopic enemies. The dirt on the germs is enough to train immune cells to produce Y-shaped blood proteins called antibodies that can detect individual foes based on unique molecular patterns.