My daughter had same thing. Went to GP and was told it was a type of eczema/psorisis and got liquid to put on overnight then wash with polytar shampoo (all on prescription). She will have to continue this once a week, to keep it a bay but it really does work!
What sort of scales do you have on scalp. Are they associated with flakiness and its more like dandruff or something else? Any itching?