Do you mean his cheeks go red and stay red for a bit after swallowing the food? Are you able to take a peek in his mouth to see if his tongue is red and/or swollen, I know that can be a hard thing to tell at this age. What foods have you tried so far that he has this reaction to?
Symptoms for allergy are usually itching of the mouth, trouble swallowing, nausea, vomiting, trouble breathing, wheezing, tummy pains, hives, eczema, weakness, lightheadedness, anaphylaxis. They don't need to exhibit all of these symptoms. My son is allergic to wheat and will have bad diarrhea within a few hours and then red splotchy eczema within 24 hours. Whereas if he has oats and/or barley, which he is also allergic to, he will have the diarrhea, eczema, and also continuous vomiting after 2 hours for an hour, then he goes pale, clammy, weak, lethargic.
So the symptoms and severity can vary, but I'd be curious as to what foods you are feeding him. Does he get any diarrhea? Gas?