My 9 month old baby got hives after eating yogurt on Friday, even though he has had yogurt almost a dozen times before. It was only his third time eating vanilla flavored yogurt, however. He has had congestion and a cough for about three weeks now and also had a fever and ear infection at the onset of the cold , which were treated with antibiotics . His congestion isn t going away, however, his temperament is fine and he is as happy as ever. I have not given him any dairy since Friday, but I m wondering how long it would take to get out of his system and whether I should try to give it to him again or have him tested for allergies after the one reaction.