If you happen to suffer from dandruff or seborrhea, selenium sulfide shampoos are one of the most effective in helping alleviate symptoms. Selenium sulfide works by providing itch relief and also lifts the scaly particles from your scalp. As with many anti-dandruff shampoos, you may have to use the product more than once to see and maintain results. Sadly, you cannot use an anti-dandruff shampoo once and expect your issue to be gone forever.