After reading the Ribo Rash Factsheet it appears this would have been the culprit.  My son's scenario was exactly the same as another child on the fact sheet with the map like raised hives all over his body and swollen eyelids and mouth.  It did take 1 week of prednisone, 2 weeks of antihistamines for the hives to disappear and a full 4 weeks for the facial flushing to go. Although I've always been careful about checking for MSG and sulphur dioxide in food since he was a baby (because he is a mild asthmatic) I had no idea that they could list something like 635 under the labelling' No MSG added'.  He did stay at my sisters the day before he reacted and ate chilli popcorn which had the No MSG labelling but now I'm fairly convinced that was it as he has been tolerating all the different natural food groups we have reintroduced him to since being on the elimination diet - he is now up to the very high list of the food groups and doing well although we still use sorbolene for bathing and moisturising as the skin on his face especially seems to be sensitive even though it's been 3 months since his severe reaction – Deborah by email