Milk might be the reason, but there are many other possibilities also. My daughter always have 濕疹 and rashes all over her body. At last I found out it was the lotion that she was using that she is allergic to. I kept on trying other brand lotions until I found one that is ok for her. There is another old fashion way that you can try, it really works. You can boil a pot of water then add 1 slice of sugar cane sugar (peeen tong) and boil until it's all melted. Then add it into your BB's bath water to take bath. It is not sticky at all and BB's skin will be more moisturize, then put lotion. Just remember if your BB is a girl, use plain water to rinse her virgina afterwards. This method works very well but it will take some time. my daughter use this sugar water for about 2 mths and her skin is really really good now.