Is the broken bit ulcerated almost? If it is my DS gets a rash very much like this from some food additives, mainly msg and similar "natural" flavours he won't get it straight away but if he's eating heaps of it. I use a cycle of moogoo, sudocream and qv cream to get rid of it. He's got scars it got so bad before we figured out what was causing it

sent from my watzamajig so may not make sense....