I had never heard of nail fungus until a few years ago when I accidentally dropped a concrete block on my foot and damaged my big toe nail.  Apart from being a yellowish color the nail didn’t bother me.  It was almost a case of “out of sight – out of mind” and I didn't know that I had contracted nail fungus.  Then I started to feel a tingling in my toe and then a mild numbness that started to spread to my foot.  So I investigated and found out that I had got nail fungus (onychomycosis) in it.  Nothing I tried cured it.  I didn’t want to use the systemic treatment because a) it is fearfully expensive, and b) it can damage one’s liver.  So much so that while taking it, one must have one’s blood monitored continually.  So I redoubled my efforts at finding a cure.  Then a Chinese acquaintance told me about an ancient Chinese remedy using vinegar.  I tried it and it worked!  I’ve also told other people about it and they too report success.
  
All you have to do is buy a bottle of white distilled vinegar, the cheapest you can find, and put two or three drops, using a cotton ear bud or an eye dropper, on the affected nail when you get up in the morning and before you go to bed.  Obviously, one does it after showering or washing one’s feet.  Just make sure that the sides and root of the nail are very well flooded.  Although my Chinese acquaintance said it isn’t necessary, I would also put a drop under (the end one cuts) the nail. 
  
The only caveat is that one must do it without fail every day.  The nail is cured when the fungus infected part has grown out completely.  The older one is the longer it takes.  Mine took more than nine months to grow out. I think it’s because as one gets older one’s nails grow more slowly.  And that’s it!
  
I don’t know how it works, but it does.  Vinegar was much used in Europe and Britain as an antiseptic in earlier days.  Remember the nursery rhyme? 

Jack and Jill went up the hill
to fetch a pail of water;

Jack fell down and broke his crown,
And Jill came tumbling after 

Then up Jack got, and home did trot,
as fast as he could caper.

They put him to bed, and plastered his head,
with vinegar and brown paper.