Dermatologist. DD has had the same thing for years and tried everything. We finally got her in to see a dermatologist (diagnosed it as *something* dermatitis) and she prescribed a whole whack of topical ointments. One's a "steroid" type oil, one's salicylic diluted in mineral oil and a different type of shampoo. If you can ask for the salicylic one NOT to be suspended in oil it would be great - I feel bad for DD because she sometimes has to go out with a oily hair and the looks she gets
Unfortunately, it's a lil time consuming because you have to apply it on your scalp much like you would if you were colouring your hair and you'd have to do it daily.
Have you tried the Ginger shampoo from the Body Shop? Another dermatologist in the city has started telling her patients to try that. So we did. While it's worked for others, it didn't work for my daughter. You might want to try that one out before you see the Dermatologist.
Hope this helps