There are several factors: 1. The blackening of the corners of the mouth is often caused by pigmentation after the healing of labyrinthitis and herpes labialis, and the pigmentation that causes the blackening will fade away slowly as long as the lips are kept healthy. 2. If the blackness at the corners of the mouth is caused by severe lack of oxygen and cyanosis, it can be relieved by oxygen therapy, such as oxygen therapy with oxygen machines or oxygen bags at home, or hyperbaric oxygen therapy at hospitals.