Dullness around the T-zone of the face and mouth may be caused by long time not cleaning the skin, endocrine disorders, seborrheic dermatitis and other reasons. 1. Long time not clean skin: face is easy to oil accumulation, hinder the normal breathing and metabolism of the skin, and easy to adsorb the dust in the air, resulting in the deterioration of the skin of the face. Long time not pay attention to clean skin will appear face T area and around the mouth dark yellow situation. 2. Endocrine disorders: unhealthy lifestyle habits such as staying up late and excessive stress can lead to endocrine disorders, which can lead to the deterioration of the facial skin and the appearance of the T-zone of the face and around the mouth of the situation of dark yellow. 3. Seborrheic dermatitis: Seborrheic dermatitis is a chronic, recurring, inflammatory skin disease commonly found in seborrheic areas of the head, face, chest and back. The T-zone of the face and dark yellow around the mouth can be erythematous and yellow greasy flaking. If you have dark yellow face T-zone and around the mouth, it is recommended to go to the hospital in time, under the guidance of the doctor to treat.