Ds is CMPI, nothing else has shown up except for Heinz light mayo (& a different catering mayo in a cafe today) causes a blotchy face /contact reaction. He has mayo a lot at home, no normal reactions to eggs/mustard. Having compared ingredients Heinz light/usual mayo, I'm down to some sort of additive but am stuck there.
Is this likely to be an allergy? And any ideas how to narrow it down to what it is?