My aim is to pass on some hard won practical experience.
All I have found on the web is confused and incomplete.
My experience is that it works as descrbed on the bottle to clean and disinfect.
The erroneous idea that it hardens skin is I think a function of the way it works not some protective or 'curing' process.
Back to my own experience.
I have been going barefoot or five fingers shod exclusively for 8 months.
Starting in the winter with the Flow model - a thicker sole unit for winter running.
After the first long run I developed blisters.
I have found that switching from shoes to not takes months and weight distribution on the forefoot changes over many months as connective tissue adapts.
I have read that all modern shoes are designed to sink into the middle of the sole, this reduces the externally visible foot, so we appear more attractive - clod hoppers no more;¬)
Based on my experience this makes the foot weakest at the point it should be strongest.
Initially most serious blistering occurred on the pad of the foot located in line with gap between big and second toe.
I used an opened safety pin cleaned with a tissue soaked in surgical spirit, pushing through the blister from close to its edge to the opposite border, placing a soaked pad over the blister and then remove the pin while applying pressure.
Apply pressure and repeat if required with an unusually large blister until it stops bleeding or weeping.
Done immediately after the run I have found myself able to run the next day.
This appears to be key, left to heal naturally it will take ages to condition your feet.
Changing to the thinner sole of five fingers KSO blistering occurred again, running more naturally now blistering had moved towards the big toe and pads of the 3rd and 4th toes.
The procedure detailed above sorted this crop out.
Recently I have been walking exclusively barefoot and ran barefoot tonight over mixed ground with lots of rough low grade tarmac some with loose stuff on a hard surface.
Predictably a new crop have appeared.
Before and after surgical spirit treatment pictures.
My experience and thinking is that the ethanol methanol mixture kills the layers of live cells exposed under the surface of the blister and so reseals the surface.
The apparent hardening of skin is superficial and lasts no longer than this new layer of dead skin, which is not long when barefoot running.
I have also noticed that the pads of connective tissue on your feet get thicker over time when running in five fingers.
Especially apparent after a long run when they are pumped up.
My running style has changed over the months to become completely neutral I assume much of this is due to removal of shoes sinking centre and was facilitated by consequentially more naturally developed connective tissue.
No injuries other than blisters when changing down sole thickness.