Jay's first allergy

Yesterday I had a few errands to run and since Jay needed to eat before we went out, I decided to kill 2 birds with 1 stone. I fixed him a plate of chicken nuggets, cut up, with a little bit of ranch dressing on them as we usually dip the chicken in ranch via a fork and putting it in his mouth. I figured, he's been doing great with finger foods and self-feeding lately so I gave him the plate and let him feed himself while I went to go get dressed. He seemed fine when I checked on him and went to go put my make-up on. All in all, it was roughly 5 minutes that he was alone, eating, and it's not like I was far away - I just in the next room.

Anyways, I get done, see his plate is empty and go to fetch him some applesauce when I notice see this rash all over his mouth, cheeks and part of his arm:

WTF?! The chicken nuggets were warm when I gave them to him, but nowhere near hot enough to give him a burn like that!

I sent this pic to my mom to get her thoughts and she said it could be an allergic reaction or some contact disease or something and to call his doctor. We've given him chicken nuggets with ranch dressing plenty of time - it's one of his regular lunch meals.

Anyways, I called his doctor's office and talked to one of the nurses. She said to hold off on giving him anymore ranch dressing for awhile and said to just monitor him for the rest of the day, see if the color on his face goes down any and that we could give him some Benadryl at bedtime. She said it sounded like an allergic reaction and that even though he's had it plenty of times before it could take awhile for an allergy to develop and show up. Mom pointed out too, that he's only had the ranch dressing given to him via a fork, straight into his mouth, no contact with his skin. I had let him feed himself with his hands, and he got it all over his mouth. Oddly though, it wasn't on his fingers... just 1 patch on his arm where he must have put it in the dressing.

He didn't seem to be in any pain though and it didn't seem to be affecting him at all. Fortunately the color went away within 30 minutes and he looked like his normal self again. I did get him the Benadryl though, gave him some before bed and got lucky that it made it him drowsy, as he conked out while drinking his bedtime bottle (the nurse said it would either make him tired, hyper or neither, so use at our own risk, lol...).