Soda tried to eat my son

So last night. O was sitting on his dad's lap. And Dad went to take a sip of soda. O decided it would be awesome to grab the can and ended up with soda all down the front of him. Dad removed his shirt and O went off to play. A little bit later, I noticed that O was scratching his stomach and when I took him to better light I found he had red welts all over his stomach and some he was scratchy until they were bloody!!! I immediately gave him some benadryl and then kept him up a little while longer to make sure his breathing was normal. The only ingredient listed in the soda that looks like it could be a problem was "caramel color" which can sometimes contain milk. Now I have never tried pouring milk on my son to see if he reacts, but I don't think I will now. That was the worst hives I have seen him have ever. There is a chance it wasn't because of the soda, but I have no idea what else it could have been. And his dinner was something he has eaten before. I hate food allergies. And just in case all you relatives want to make sure that this doesn't happen on your watch, the name of the soda rhymes with Tepsi.