I have been asking that question for almost 4 years now. My little girl had it since she was a few months old. It was even misdiagnosed as ringworm of all things! But we were lucky to get in touch with a great pedia-derma who also had the same complaint since she was a little girl as well, so I felt we were in good hands.
Believe it or not, just a few teaspoons of Virgin coconut oil and we were able to see marked improvement. My mother recommended we us Peter Paul because she saw it featured in a TV show and according to her their process and plant is very sanitary.