IMO, they seem to spread when they pop because it causes the areas surrounding the open sores
to remain moist. Add a little heat
and suddenly it becomes a new patch of blisters
. Very frustrating. I find myself needing to take my shoes off under my desk at work frequently to ventilated them and prevent them from coming in the first place. But, inevitability, there comes a day or three where I am stuck in hot shoes for too long...