MEDICALLY KNOWN AS. Seborrheic dermatitis is a common infant condition. However, adults can get it (dandruff) as well. Treatment is a shampoo with salicylic acid, selenium sulfide, coal tar or zinc pyrithione. Use daily for a week or so, then cut it to 2-3 times a week. Leave it in place for 5 mins or so after gently massaging the scalp, then rinse.