I found this a while back somewhere and filed it for future reference:
“I heard that vinegar had some healing properties so I decided to
put it to work on my toe. I roughed up the nail a bit with an
emery board, then began soaking my foot in vinegar. Not much, just enough to cover my toes. I did this about once or twice a week fora few weeks. Also, I would soak a cotton ball in vinegar, squeeze it out, place it on top of the toenail and adhere it with a Band-Aid. I would do this if I wasn’t leaving the house for an afternoon or before I went to bed at night.
Literally, within a week I noticed new nail appear, replacing the
old nail. My entire big toe had been a mess, but after only a handful of these treatments, my toenail looks completely normal, as if nothing ever happened to it.”