Open mouth breathing can still be corrected at age thirty. Adults with open mouth breathing can be corrected by treating the cause of the problem and wearing a respiratory device. 1. Causal treatment: Open-mouth breathing in adults in their thirties may be caused by chronic rhinitis, sinusitis, enlarged adenoids or enlarged tonsils, etc. Therefore, patients can go to the otorhinolaryngology and stomatology departments of hospitals for examination, and after clarifying the cause of the disease, they should actively treat the primary disease, and then the open-mouth breathing situation can be corrected. 2. Wear respiratory corrective device: if exclude disease factors, has not been corrected open-mouth breathing, mostly caused by bad habits, can be under the guidance of the doctor to wear movable orthodontic devices, to prevent open-mouth breathing, and promote the patient to gradually develop the habit of breathing through the nasal cavity. The above methods can generally correct the situation of open-mouth breathing in adults in their thirties. If not corrected in time, long-term open-mouth breathing can easily lead to maxillofacial deformities, dental deformities, respiratory diseases and other hazards. 3. Orthodontics and orthognathics: Orthodontics and orthognathics can improve the face of open mouth breathing, and play a certain role in maintaining the effect of open mouth breathing after treatment. Adult patients with open mouth breathing should go to the hospital as soon as possible for examination to exclude disease factors and choose the correction method under the doctor’s guidance to avoid delays that may cause adverse consequences.