Dawn Dish Soap
Rub it in every other day. Let it stand for 15 minutes on the scalp and then rinse out. Repeat for a few weeks.
Simple, inexpensive--I tried to find one that smelled the most like shampoo and least like dish soap. And, well, it seems to be working!
My youngest child's cradle cap is finally gone and my middle child's is finally mostly gone.
Just thought I'd pass this on in case it might be of help to someone--and save them a trip to the dermatologist!