reversible like this. By bypassing the outer or middle ear, BAHA can increase hearing in noisy situations and help localise sounds. In addition to improved speech understanding, it results in a natural sound with less distortion and feedback compared with conventional hearing aids. The ear canal is left open for comfort, and helps to reduce any problems caused by chronic ear infections or allergies. In patients with single-sided sensorineural deafness, BAHA sends the sound by the skull bone from the deaf side to the inner ear of the hearing side. This transfer of sound gives a 360° sound awareness. BAHAs may facilitate normal speech development. Chronic ear disease This fairly common condition is often associated with continuous or intermittent drainage from the ear canal. These patients may also have a hearing loss and need amplification. A conventional air conduction aid with a mold placed in the ear canal opening may not be appropriate due to the drainage, and may even provoke drainage. If the hearing loss is significant an air conduction aid may have difficulty overcoming the dysfunction of the eardrum and middle ear bones. Bone conduction hearing device bypassing the middle ear may be a more appropriate treatment for these patients. Good transmission of sound in the bone, with reduced attenuation and distortion may be possible. Single-sided deafness A person with unilateral hearing loss may have functional difficulty hearing even when the other ear is normal, particularly in demanding situations such as noisy environments and when several people are speaking the same time. A complication in single-sided deafness is hearing impairment in the hearing ear. Conventional ear surgery involves a risk of hearing loss due to the surgical procedure. Most ear surgeons are thus reluctant to perform surgery on an only hearing ear. The BAHA surgery avoids this risk and may be an appropriate treatment. An extended trial of a BAHA system with a headband prior to surgery led to more realistic expectations. In the trial, 50% of the candidates wished to proceed to surgery. External ear canal problems Irritation in the external ear canal due to inflammation or eczema may be a condition for which a conventional air conduction aid is not an appropriate treatment. Direct bone conduction may be an option. Malformations Patients with malformations are not always suitable for reconstructive surgery. Treacher Collins syndrome patients may have significant malformations with ossicular defects and an abnormal route