Snapshot A 34-year-old woman presents to the dermatology office for excessive dandruff. She reports that she has been dealing with this issue for the past 2 months. She is concerned that the dandruff is extending to her face now. On physical exam, there is flaking and some erythema on her scalp, posterior neck, and forehead. She is diagnosed with seborrheic dermatitis and given a topical agent to help with the symptoms. (Seborrheic dermatitis) Introduction Drugs selenium sulfide topical found in over-the-counter shampoos Mechanism of action disrupts mitosis, resulting in decreased turnover of epidermal cells and decreased flaking also has mild antibacterial and antifungal activity Clinical use seborrheic dermatitis pityriasis versicolor Adverse effects skin irritation