I’ve been suffering from the Athlete’s Foot fungus off and on for a while despite treatment and I reckon I’m getting reinfected from one shoe. So how can I kill off the fungus living in that shoe without damaging the shoe? There’s no visible fungus in the shoe.
There are plenty of sprays that claim to kill the stuff that’s living in your shoe. Take out the sock liners/footbeds to make sure you’re getting everything and give it a good spritz. Might was well replace the liners while you’re at it.
Depending on the shoe you may be able to wash and dry it (most running shoes are washable, they’re all synthetics these days). I’ve dunked my trail runners in water with a little bleach, hosed them off and then set them outside to dry. Obviously not recommended for nice leather shoes.
When I had this problem I used an athlete’s foot powder that contained tolnaftate. I used a tolnatate cream on my feet (twice a day IIRC) for two months and when that was done, I used the powder in my shoes every day until I had used up the container, which I think took about a month. You have to be persistent because that fungus can hide in a corner of your shoe or under a toenail and flare up again months after you think you’ve wiped it out.