Hey mate, I too discovered this by chance and the feeling I get is like no other I have experienced, is just simply amazing, my eczema is on my hands so easy for under a hot tap, the problem I find is the next day these "bubbles"or pustules form under the skin and slowly surface and they are itchy as hell so for ten seconds of euphoria I suffer three days of really crappy skin and intense itching, pretty much self harm, do you get these? Makes me try to avoid it but sometimes I have to just burn away, I find it best while the water gets hotter so starts off warm and I can pull my hands out just before they actually burn.
I too wonder about the mechanism, I guess that it's an cllmax, simply a feeling that reaches unbearable levels and then a release, in this case the heat makes the itch worse until it can't itch any more, not one hundred percent on that one though! Would like to hear others thoughts