My two personal cents...
I'm a chronic nail bitter.... While I'm very good with my own personal hygiene, I don't just live at home. I don't get sick very often, but for when I have visited a hospital - Laid me out, twice....
Other than that, I have my down days, but with rest and maybe a confident belief in Airborne, I keep going.
I've had a couple of dentists as clients in my IT job... I try to wash my hands before I leave, but....
I think the more germs you ingest as a little tyke, the better...