Re: What my vet said...

PPS obviously, any contamination by pathogens resulting in disease is, in a way, caused by the immune system's response, or rather lack of a coherent or sufficient one. However, extra contamination from external sources does certainly help speed it along.

Just look at all those people who get toenail fungi from pools, locker rooms, or people that they cohabit with. The difference with skin fungi is that they are less obvious and harder to identify - a rash is just a rash to people, while weird crap on your nails is definitely 100% for sure fungus.

Btw, the only reason gut yeast "isn't" all that infectious is that we generally don't touch other people's faeces. Otherwise, given the right moment (such as a lapse in health, stress, whatever) and environment (moisture, carbs, etc), and ALL pathogenic yeasts are infectious as hell.