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.
Conductive hearing loss developing during childhood is usually due to otitis media with effusion and may present with speech and language delay or difficulty hearing. Later onset of conductive hearing loss may have an obvious cause such as an ear infection, trauma or upper respiratory tract infection or may have an insidious onset related to chronic middle ear disease, otosclerosis or a tumour of the naso-pharynx. Earwax is a very common cause of a conductive hearing loss which may present suddenly when the wax blocks sound from getting through the external ear canal to the middle and inner ear. Diagnosis
Diagnosis requires a detailed history, local examination of the ear, nose, throat and neck, and detailed hearing tests. In children a more detailed examination may be required if the hearing loss is congenital. Otoscopy
Examination of the external ear canal and ear drum is important and may help identify problems located in the outer ear up to the tympanic membrane. Differential testing
For basic screening, a conductive hearing loss can be identified using the Rinne test with a 256 Hz tuning fork. The Rinne test, in which a patient is asked to say whether a vibrating tuning fork is heard more loudly adjacent to the ear canal (air conduction) or touching the bone behind the ear (bone conduction), is negative indicating that bone conduction is more effective that air conduction. A normal, or positive, result, is when air conduction is more effective than bone conduction.