How do you treat/kill toe nail fungus?
The OTC topical creams really do work, so use that when needed. Then, dig deeper to determine if you have yeast or fungus inside of you that is exacerbated by moisture in the shoe or sock. This may be your signal that there is a deeper issue brewing. Investigate Candida (yeast) on the web, and see if any symptoms ring true for you.
Treat this both internally and externally – one leads to the other in the cause and the cure.