Mystery Reaction

Last year Tanner had an allergic reaction to...something... We still have no idea what. At the time the allergist decided it was Ideopathic Uticaria (because all his allergy tests were negative) or in other words...Hives that come and go for no reason "na na na na na na". But since then he has had no problems. But now I am pretty sure he is allergic to something. A couple of weeks ago our babysitter called to tell us tanner was throwing up everywhere after giving him some chocolate milk- a few days later he threw up when we gave him yogurt- I would say 'milk' except he drinks milk and eats cheese daily with no problem- so maybe he is lactose intolerant? possibly- who knows. We wait and see- then sunday morning He got up before we did (so I only have the words of tanner and cristine as to what happened) he got a carrot and cristine opened a small bag of potato chips for him- then came to tell us that tanner was very itchy. Here are his hives.

They did get worse after this and spread very quickly to his feet and hands. but we were too busy getting him taken care of and watching him to get more pics.

So, I think it was something on the stool he climbed on as there were no hives around his face or mouth...and they were mostly clustered around his knees and arms... again the answers continue to allude us. We haven't taken anything out of his diet- and he continues to eat fine. ideas??