Usual Adult Dose for Seborrheic Dermatitis Selenium sulfide topical 2.25% shampoo: Use twice weekly until symptoms are controlled. Then weekly, every 2 weeks, every 3 to 4 weeks. Do not use more frequently than needed to control symptoms. Selenium sulfide topical 1.00% shampoo: Shake well. Shampoo and rinse thoroughly. For best results, use regularly at least twice a week or as directed by a doctor. Selenium sulfide foam: Apply to affected area twice a day. Selenium sulfide foam should be rubbed into the skin until it is completely absorbed. Shake well and invert to administer. Usual Adult Dose for Tinea Versicolor Selenium sulfide topical 2.25% shampoo: Apply to affected areas and lather with a small amount of water. Allow the product to stay on the skin for 10 minutes, then rinse thoroughly. Repeat this procedure once a day for 7 days or as directed by a physician. Selenium sulfide foam: Apply to affected area twice a day. Selenium sulfide foam should be rubbed into the skin until it is completely absorbed. Shake well and invert to administer.