9 months baby mute voice may be physiological factors, may also be acute infectious laryngitis and other pathological factors. 1. physiological factors: due to the 9-month-old baby vocal cords and other organs of articulation are not yet fully developed, after a long time screaming or crying will cause congestion and edema in the throat, resulting in a mute voice. It is recommended to appease the emotions of 9-month-old babies to avoid excessive use of the voice. 2. Pathological factors: If the 9-month-old is infected by bacteria or viruses that cause acute diffuse inflammation of the mucous membrane tissue of the larynx, resulting in acute infectious laryngitis, triggering the 9-month-old’s mute voice. 9 months baby voice mute, there may also be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.