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Seborrheic dermatitis occurs as a result of an overproduction of skin cells and sebum, the skin’s natural oil. However, the exact cause of this process is unknown. It appears to be associated with an overgrowth of a normal skin yeast fungus, but experts are unsure whether the fungus causes flaking or skin flaking allows for the overgrowth of the fungus.

In many cases, seborrheic dermatitis appears to be related to family history and is more common in people with oily skin and hair. In some cases it is associated with psoriasis or acne. People who live in northern climates may experience seasonal flare-ups when the weather turns cold and the air becomes drier, with remission occurring in the summer months. African Americans, however, are more likely to flare-up in the summer months. 

Other factors known to trigger seborrheic dermatitis include:

• Stress
  
• Fatigue
  
• Illness
  
• Infrequent hair and skin cleaning
  
• Use of lotions that contain alcohol
  
• Obesity
  
• Hormonal changes

Several conditions also are associated with seborrheic dermatitis. They include:

• Neurological conditions, such as Parkinson’s disease, epilepsy, head injuries and stroke
  
  
• Medical conditions that stress the body, such as heart attacks
  
  
• Immune system disorders, including human immunodeficiency virus (HIV)
  
  
• Vitamin B deficiencies