Since your dandruff has lasted five years, it is likely a condition called seborrheic dermatitis. I recommend using medicated shampoos with active generic ingredients like ketoconazole (2%), ciclopirox, or selenium sulfide. For heavy scaling, shampoos containing salicylic acid or coal tar can help. For the best results, massage the shampoo into your scalp and leave it on for 5 to 10 minutes before rinsing. You can alternate between two different active ingredients weekly to prevent your scalp from getting used to one. If these options do not work, please see a dermatologist, who can prescribe topical mild steroids or antifungal lotions to safely clear the scalp.