Hello. Thanks for writing to us at healthcaremagic Dandruff if excessive or resistant to regular OTC shampoos can be due to some other cause like seborrheic dermatitis or scalp psoriasis. While seborrheic dermatitis is associated with itching and yellow greasy adherent scales, psoriasis is characterized by well defined patches, with thick scaling, commonly involving the hair line. In psoriasis there may plaques elsewhere on the body. The diagnosis is clinical, therefore a visit to a dermatologist would be useful in that regard. You may use an OTC antifungal shampoo e.g 2% ketoconazole, alternate days, lather it well and leave it for 5 minutes to act before rinsing it off. If this does nt seem to help you may seek an appointment with a dermatologist for a confirmatory diagnosis. You dermatologist might also put you on topical steroid lotion for a period of about 2 weeks, if he or she feels that there is too much scaling and a shampoo alone might not be sufficient. Thereafter once the scaling is effectively controlled with topical steroid lotion, a shampoo would be effective for maintaining the improvement. Regards