Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). If a conductive hearing loss occurs in conjunction with a sensorineural hearing loss, it is referred to as a mixed hearing loss. Depending upon the severity and nature of the conductive loss, this type of hearing impairment can often be treated with surgical intervention or pharmaceuticals to partially or, in some cases, fully restore hearing acuity to within normal range. However, cases of permanent or chronic conductive hearing loss may require other treatment modalities such as hearing aid devices to improve detection of sound and speech perception. Causes Common causes of conductive hearing loss include: External ear Cerumen (earwax) or foreign body in the external auditory canal Otitis externa, infection or irritation of the outer ear Exostoses, abnormal growth of bone within the ear canal Tumor of the ear canal Congenital stenosis or atresia of the external auditory canal (narrow or blocked ear canal). Ear canal stenosis & atresia can exist independently or may result from congenital malformations of the auricle such as microtia or anotia. Acquired stenosis (narrowing) of the external auditory canal following surgery or radiotherapy Middle ear Fluid accumulation is the most common cause of conductive hearing loss in the middle ear, especially in children. Major causes are ear infections or conditions that block the eustachian tube, such as allergies or tumors. Blocking of the eustachian tube leads to decreased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles and the tympanic membrane. Acute or Serous otitis media Chronic suppurative otitis media (CSOM) Perforated eardrum Tympanosclerosis or scarring of the eardrum Cholesteatoma Eustachian Tube Dysfunction, inflammation or mass within the nasal cavity, middle ear, or eustachian tube itself Otosclerosis, abnormal growth of bone in or near the middle ear Middle ear tumour Ossicular discontinuity as a consequence of infection or temporal bone trauma Congenital malformation of the ossicles. This can be an isolated phenomenon or can occur as part of a syndrome where development of the 1st and 2nd branchial arches is seen such as in Goldenhar syndrome, Treacher Collins syndrome, branchio-oto-renal syndrome etc. Barotrauma, unequal air pressures in the external and middle ear. This can temporarily occur, for example, by the environmental pressure changes as when shifting altitude,