The causes of seborrheic dermatitis are poorly understood. Since this condition tends to occur in areas of heavy sebum production, it is felt that oily skin may be a factor leading to seborrheic dermatitis. In addition, it seems that many patients with seborrheic dermatitis have excessive growth of a normal skin yeast (Pityrosporum or Malassezia) in the affected areas. Whether this common microorganism really leads to seborrheic dermatitis or is just a secondary phenomenon remains to be determined.
The fact that topical antifungal medications are effective in controlling this disease has led some to conclude that this is a fungal condition. However, this theory is not yet accepted.