What else was in that batter? Has he eaten ONLY egg at some point to determine if it's the egg he's allergic to?I know you're not trying to say they do, I'm
just making sure you know that they don't.
When my brother got this egg rash, we hadn't eaten eggs in over a week. Then mom put only 2 eggs in a really big batch (2 eggs mixed into several gallons worth of batter) of something she was making. That's when he's rash showed up, after he ate some of that.
I don't know if raw eggs has anything to with egg allergies, but we also don't eat raw eggs.
Just thought it might be helpful to know that.
Could be a gluten allergy or reaction to something else in the batter.