All shampoos have some detergent action and may be more effective if used more often. Another trick in treating bad dandruff is to leave the shampoo in prolonged contact with the scalp. For example, wash hair, rinse, and reapply shampoo, then apply a shower cap for 30-60 minutes, then do a final rinse. These may reduce itch. Salicylic acid shampoos like T-Sal, Ionil, and Sebulex mobilize scale or chemically scrub your scalp.
Selenium sulfide kills yeast and inhibits cell turnover.
It is about equally effective compared with zinc shampoos, though it may work when other agents fail. It has a pleasant odor. Any shampoo may work when another fails. It is important to experiment. If your dandruff is inflammatory, itchy, or unusually severe, then a prescription steroid lotion or solution like Temovate, Lidex, Synalar, betamethasone valerate, or Dermasmoothe may be the answer.