Chase's Hives

Chase had to come home from school one day because he started to break out in hives all over his body. After two days it ended in an ER visit. We still to this day, don't know what caused them. They had pajama day at school that day. And they only thing I could think of is, the thrift store pj's he was wearing weren't washed well enough and had some cat or dog dander on it. :( They didn't seem to bother him too much. He said it hurt a little. And his skin was hot. So we knew it was an allergic reaction to something. I just wish I knew what caused them.