What causes black discharge from mouth during sleep?

Black discharge from the mouth during sleep can be caused by several factors, including the presence of blood that has oxidized and turned dark, oral infections, or the presence of certain medications that can lead to dark pigmentation. Additionally, poor oral hygiene can contribute to the buildup of bacteria and food particles, which may result in discoloration. If this symptom occurs, it is important to consult a healthcare professional for proper diagnosis and treatment.