• Viruses, genetics and existing drugs triggers hairs in the inner ear to regrow
• These hairs pick up on noises as they enter the ear and send signals to the brain
• Hairs can also get lost due to infections and diabetes, and are not then replaced

Deafness could be reversed, research suggests.

Scientists have discovered how to regrow cells in the ear that are critical for hearing.

Viruses, genetics and even existing drugs could trigger little hairs to regrow in the inner ear, according to a study by the University of Rochester.

These hairs are the first step in picking up on noises and are not naturally replaced when killed off by age or overexposure to loud noise.

Humans do not regenerate hair cells in the inner ear once they are lost, which leads to permanent hearing damage.

These hair cells move in response to vibrations, which causes nerve impulses to be sent to the brain where they are interpreted as sounds.

In other animals, however, such as birds, frogs and fish, surrounding cells in the inner ear, known as the cochlear, can change into hair cells. 

Although unclear exactly how this occurs, it is thought to be driven by protein signalling.

'It’s funny, but mammals are the oddballs in the animal kingdom when it comes to cochlear regeneration,' study author Dr Jingyuan Zhang said.

WHAT CAUSES HEARING LOSS? AND CAN IT BE TREATED?

Hearing loss can be temporary or permanent.

It can also develop gradually with age or come on suddenly.

Hearing loss in just one ear may be due to a build up of wax, an infection or a burst eardrum.

Sudden loss in both ears may be due to damage from a very loud noise or side effects of certain medication.

Gradual hearing loss may be the result of fluid building up, known as glue ear; a bony growth, called otosclerosis; or skin cell accumulation, known as cholesteatoma.

Gradual hearing loss in both ears is usually caused by ageing or exposure to loud noises over many years.

Hearing loss sometimes gets better on its own.

A build up of wax can also be treated by being suctioned out or softened with drops.

However, hearing loss can also be permanent, with treatment then focusing on making the most of the hearing that remains.

This may involve:

• Hearing aids
• Implants - attach to the skull or are placed deep in the ear, if hearing aids are ineffective
• Communicating via sign language or lip reading

Hearing loss can be prevented by avoiding loud music and wearing headphones that block out background noise.

Ear defenders should also be worn if you work in a noisy environment, such as a building site.

And ear protection should be worn at concerts and other noisy events. 

Source: NHS Choices

The researchers analysed the effects of one of these proteins, known as ERBB2, in the hair cells of newborn mice. 

Previous studies suggest ERBB2 is involved in the production of new hair cells.

Results of the new trial confirmed surrounding cells that expressed ERBB2 were more likely to become hair cells.

The scientists then tested the effects of viruses that trigger ERBB2 production.

They also genetically modified the mice to over-express ERBB2 and gave them drugs that are known to activate the protein. 

These drugs are already used to stimulate cell regeneration in the eyes and pancreas.

All these methods led to greater hair cell production. The study was published in the European Journal of Neuroscience. 

'The process of repairing hearing is a complex problem and requires a series of cellular events,' lead author Professor Patricia White said.

'You have to regenerate sensory hair cells and these cells have to function properly and connect with the necessary network of neurons.

'This research demonstrates a signaling pathway that can be activated by different methods and could represent a new approach to cochlear regeneration and, ultimately, restoration of hearing.' 

Hearing loss affects around 37.5 million people in the US and 11 million in the UK to some extent.

It is a normal part of getting older but can also be triggered by viral infections, diabetes, ear injuries and overexposure to loud noise.

This comes after research released earlier this year suggested children who were exposed to smoke in the womb and as babies are more than twice as likely to be deaf. 

Nicotine interferes with chemical messengers in the nerve that tells the brain what sound it is hearing. Smoking may also irritate the lining of the middle ear.