The reading here is a bit weird. It's like the words 裸 (はだか) and 足 (あし) were smushed together into one word. The 裸 becomes はだ and the 足 becomes し. You can think of it this way: You were barefoot too long, and because of this, you don't have feet anymore, though you had ashi (はだし) at one point in the past.
You shouldn’t wear slippers barefoot if you don’t want to get athlete’s foot.