Sensorineural Hearing Loss

Most hearing loss is caused by things in life that are often unavoidable – exposure to loud sounds, getting older, infections, certain medications and sometimes suddenly, without a known cause.

Hearing loss can occur in a few different ways. It can occur from problems with the outer and middle ear (conductive hearing loss), from problems with the inner ear (sensorineural hearing loss) or from a mix of both.

Sensorineural hearing loss, or damage to the hair cells or nerve fibers of the inner ear that convert sound into electrical impulses, is the most common form – accounting for 90% of all hearing loss. The damage can be congenital (present at birth, often hereditary) or acquired later in life.

Currently there are no FDA-approved treatments to repair this sensory system. Frequency is developing small molecule therapeutics designed to regenerate hair cells lost to acquired SNHL.

Understanding the Causes of Acquired SNHL

Noise exposure
Ototoxic medications
Sudden and unexplained

A single loud event – firecrackers or standing too close to a speaker at a rock concert with unprotected ears – can cause hearing loss. At the same time, noise exposure can gradually damage the hair cells and nerve fibers over time.

Most of us are exposed to a lot of noise during our lifetime, and the risk of hearing loss is growing as the world gets louder and lifetimes get longer.

Other causes of acquired sensorineural hearing loss include disease – viral infections, immune system problems, trauma – and toxic exposures to certain medications.

Sensorineural hearing loss can also occur suddenly and without explanation. Individuals may wake up one morning with lost hearing, typically on one side, or the sudden loss may occur over a few days. Only about 10 percent of people diagnosed with sudden SNHL can pinpoint an identifiable cause.

The Challenge of Treating Sensorineural Hearing Loss

We have two different types of hair cells in the cochlea – inner hair cells and outer hair cells.

Outer hair cells sense and tune sound, as well as filter out any unwanted sounds. Inner hair cells convert mechanical sounds into electrical signals that are carried to the brain by the auditory nerve.

Today’s treatments for hearing loss – amplifying devices such as hearing aids – are limited in their ability to improve sound clarity, as they don’t treat the inner ear at all and cannot replace the tuning and filtering of lost hair cells.

Additionally, most acquired SNHL begins in an area of the cochlea responsible for high frequency hearing, which is often out of reach for amplifying devices. High frequency hearing loss is associated with problems understanding speech and recognizing words, especially in noise.