How does a baby's immune system develop?

Anthony L. Komaroff, MD
Internal Medicine
During birth, babies emerge from a sterile, germ-free environment in the womb and rapidly pick up the bacteria and other microbes from the mother's birth canal and then from the world at large. In those early months, a child's immune system develops and responds to the microbes it encounters. In the process, the immune system "learns" to identify billions of different kinds of microbes. It makes sense that these particular microbes, which differ from person to person, influence how the adult immune system will ultimately function in each person.

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