Failure to pass the left ear in infants is what is referred to clinically as failure of one ear of the newborn hearing screening, and can be caused by a variety of causes, whether in the outer, middle or inner ear. Common causes include narrowing or atresia of the external ear canal, blockage of the ear canal with cerumen or fetal fat-like secretions, poorly pneumatized middle ear cavity, congenital malformations of the middle and inner ear, such as cochlear anomalies, large vestibular canal syndrome, or unilateral auditory nerve dysfunction due to genetic mutations. In case of failure of monaural hearing screening, regular hearing re-screening and audiological confirmation are required according to the prescribed process to detect the problem as early as possible for early intervention and treatment to avoid affecting the speech development of the affected child.