Open mouth breathing is usually reversible after 16 years of age when corrected (by treating the cause, surgery, mouth closers, etc.). There are many causes of open-mouth breathing, including various causes of nasal insufficiency such as rhinitis, and obesity. Prolonged open-mouth breathing can lead to ugly facial features, such as abnormal development of the jawbone and a sunken mouth, known as “adenoidal facies”. Open mouth breathing can be corrected by treating the cause of the problem, wearing a mouth closure device, etc. Those with altered facial features can be corrected by surgery, which is usually reversible. It is advisable to consult a hospital as soon as open-mouth breathing is detected, as the earlier treatment is given, the better the outcome may be, to avoid delaying the condition.