Irritation or food allergy?

How can you tell the difference? My 15month son developed this while eating lunch. A bean& cheese quesadilla with a mild salsa. I noticed redness while he was eating but figured it just the red salsa. After lunch I wiped his face and noticed it was actually irritated. About an hour now it’s faded and his cheeks are rosy. I’m assuming the salsa just caused some irritation. He doesn’t seem bothered.

The first pic is right after lunch.

The bottom is about 5 minutes after lunch