Infant Food Allergies

Hi real quick I'm concern my 7 month baby been eating banana occasionally... I barely notice today that a mouth rash he gets could be related to the banana. I breastfeed him as well and I initially thought that the rash was maybe a reaction to any of the products I was bathing with thinking maybe I'm not rinsing good enough but I have been trying my best to not have any product residue in my breast. Now I gave him banana today and he has again a rash. I really haven't heard much of babies having an allergic reaction to bananas. Could I be right or what else could it be? Please help me. My baby seems normal just with a rash in his mouth and some on his belly.