Boric acid still makes nervous but it is completely safe?
It's not toxic otherwise. You need very high concentrations: lethal dose is 2.6g/kg. To put that in perspective, table salt is lethal at 3g/kg.
Wouldn't that lead to a powdery build up after a while? Do you need to eventually shake out the powder?
Best is to try it and make your own experience. Boric acid is quite cheap.
That's like a human eating about 2g of the stuff every day, on par with your needed daily intake of salt. That would be a lot of boric acid...
In our case were only concerned with external application and there doesn't seem to be any noted effect there.
I've had fungal infections in the past, between the toes mostly, but it's a thing of the past now. Nothing in the past 5 years.
Have a look at Big Clive's video on "Fixing your feet":
I started doing this a few years ago after watching a video from Big Clive where he mentioned it, and it has really made a difference. No more smelly shoes, socks or feet and no fungal growth.
Seems silly but living under the tropics and macerating in closed shoes all day does have these rather annoying side effects, and whatever shoes you wear, sweat and a warm environment are a breeding ground for bacteria.
Adding about half a teaspoon of powdered boric acid to each shoe at least a couple times a week makes a huge difference.
Best is in new shoes, they will smell like new even a couple of years later. I'm not even exaggerating when I say that at the end of a long day, socks only smell of fabric softener and feet smell of well, nothing.