It could also be that the nerves don't actually repair themselves, but your body adjusts to the lack of sensitivity and amplifies signals from a few surviving neurons. So every injection would kill more of the neurons, and at some point it is permanent.
I wondered if this was the case too. I’m also curious the mechanism this uses, what’s mentioned in the article (flood of calcium into the nerve ending) doesn’t make sense to me, but I have no expertise in this field.
