Look in the mirror and you won't see your microbiome. But it's there with you from the day you are born. Over time, those bacteria, viruses and fungi multiply until they outnumber your own cells 10 to 1.
As babies, the microbes may teach our immune systems how to fight off bad bugs that make us sick and ignore things that aren't a threat.
We get our first dose of microbes from our mothers, both in the birth canal and in breast milk. Family members tend to have similar microbiomes.