I recently read the book "Invisible Friends," and in it, among other things, the author does go on to explain that it's theorised that many skin infections come from a lack of biodiversity in a persons' skin microbiome, because the "good" or neutral microbes compete with the "bad" for resources. Supposedly people who share a house together often have similar gut microbiomes, too.

So yeah, I don't know. I think you have a point here.