Seborrheic dermatitis or dandruff is usually indicated by itchy flaky scalp to give it a more common name. Doctors at the Mayo Clinic say you can treat dandruff by using a medicated shampoo, but be aware that you may need to switch brands from time to time, as individual products may lose their effectiveness. Ideally, wash your hair with the shampoo every day or so, and make sure it actually comes into contact with your scalp by leaving it for a few minutes.
But don't use the medicated brand exclusively for it tends to be harsh on the hair. Instead, alternate it with a regular shampoo and make sure you use a conditioner as well. And if your scalp doesn't clear up within six weeks, it's worthwhile seeing your doctor for either a prescription shampoo or a topical medication.