Why does warm water hurt on cold hands?

I guess it's partly because the cold itself produces quite profound chemical changes in and around the nerves that report pain messages, and that's why anybody who's had cold hands for a long period of time will describe how intensely painful it is. So I suspect that it's because the nervous system is already in a sensitised state when one adds another signal to those nerves. What nerves do that aren't behaving properly is they misinterpret sensory information, and so my guess is that partly what's happening is that you've got nerves that have been upset by the cold and when you apply a warm stimulus, it might be interpreted as being painful. This doesn't necessarily mean that it's damaging. It may also be something to do with mixed signals going to the brain, so you have messages coming that they are very cold, but then you get a mixed signal about another sensation coming in. Often these signals can be interpreted as pain. I don't know if that's the right answer but that's what I would guess.