Our immune systems need interactions with good bacteria to work, which partly lies on physically meeting people and touching them. 

Our current obsessions with avoiding physicial encounters with germs are not only slaying off "bad" bacteria, they're also massively killing the ones that are good for us.

In the long run, we may even make some really important microbes go extinct.

It's still a hypothesis, though. As long as doubt remains, we should all keep on washing our hands, putting on these pesky masks, and, yeah, also eating a healthy diet and doing exercise!