selsun blue hair shampoo for treating dandruff. selsun blue shampoo contains selenium sulfide, which is used on the scalp to help control the symptoms of dermatitis and dandruff. It is characterized by being antibacterial and has mild antifungal activity. Selenium sulfide at a concentration of 2.5% is also used to treat pityriasis versicolor, which is a type of skin fungal infection.