My son had terrible cradle cap that went from his eyebrows straight back to the crown of his head. It was terribly thick and crusty. Everytime I would wash it off it would be back by the next morning. I tried olive oil, coconut oil, Oil of Oregano, Apple Cider Vinegar etc. With no avail.
It then occured to me that perhaps Kombucha's acidity and probiotics might help. So the next bath I washed of the cradle cap secretions and put a fresh kombucha scoby on top of his head and left it there for 10 or 15 minutes, then rinsed his head with water. The next morning his head was smooth and shiny bald (the cradle cap was retarding hair growth). The cradle cap was completely gone and two months later it is still gone, replaced with a headful of hair and an impeccably healthy scalp!