Seborrhea is a skin disorder resulting from the accumulation of sebum on the skin. It is more severe than common dandruff. I have a friend with a full head of thick hair who has used Head and Shoulders and Head and Shoulders Therapeutic for 50 years (he is 69), and it hasn't affected his locks one bit. I, on the other hand, am bald and didn't use it. That is my two cents' worth understanding as I am not a dermatologist or doctor of any other type.