Each person has around 15,000 hair cells in each ear, which are vital for converting sound waves into brain-bound electrical signals that we perceive as noise.
[Source: Flickr – Karen Nichols (Wessex Archaeology) (6 December 2011) ‘1 How We Hear Sound’]
Deafness can develop following the death of these inner ear hair cell structures (sensorineural hearing loss) and this process can be caused by exposure to excessive sound pressure levels.
At present, there is no cure for noise-induced hearing loss (NIHL).
However, a recent systematic review and meta-analysis of multiple studies, published in the Military Medicine journal, has indicated that steroid treatment, with or without hyperbaric oxygen therapy (breathing oxygen in a pressurised tank), appears to improve hearing thresholds post-acoustic trauma.
We have also previously reported on preliminary experimental successes with nicotinamide riboside vitamin (here), a drug cocktail that matures inner-ear stem cells into auditory hair cells (here), cyclin-dependent kinase 2 enzyme inhibitors (here), seizure-inhibiting zonisamide (firstly, here, and then again, here) and cancer-treating dabrafenib (here), in several past editions of BC Disease News.
Another line of clinical investigation has focused on infrared (IR) light, or near-infrared (NIR) light, which could be able to both prevent hair cell death and trigger repair.
As primary evidence of positive therapeutic effect, Basta et al (2020) found that mice treated with NIR light for 10-minutes prior to loud noise exposure experienced less hearing loss than untreated test subjects, showing ‘significant protection’.  Equally, Rhee et al (2012) examined noise-exposed rats that had been supplied with IR light in the left ear (the right ear did not receive IR) for 60-minutes for up to 12 consecutive days. After the 12th irradiation, hearing threshold levels were ‘significantly lower’ for the left ear than the right ear. There was also a ‘significantly larger’ number of hair cells visible under an electron microscope in treated ears.
It is suggested that IR and NIR light provide auditory relief by interacting with a protein, called ‘cytochrome c oxidase’, which increases production of adenosine triphosphate (ATP). Research has shown that higher levels of ATP compound reduce cell death and activate cell repair processes. Raised ATP levels also reduce inflammation, which is a factor implicated with noise-induced deafness.
Building on initial-stage findings in early-stage animal trials, The Daily Mail reported earlier this month that academics at the University of Miami, in collaboration with the Office of Naval Research, have begun a clinical trial that will be assessing the efficacy of delivering NIR light into human ears.
100 healthy individuals have been recruited to take part in the study, led by Professor of Otolaryngology, Michael Hoffer, which has an estimated completion date of March 2022.
The participants will be subjected to safe levels of noise exposure on 4 occasions. On 2 of the 4 occasions, they will be administered with NIR light for 30-minutes-per-ear. For the remaining occasions, ‘sham light therapy’ (the control) will be administered.
Various tests will then be undertaken to ascertain the effects of NIR light on the behaviour of hair cells.
- Changes in auditory threshold by measuring air conduction thresholds from 0.5 kHz up to 8 kHz.
- Changes in otoacoustic emissions through appropriate testing
- Changes in central auditory performance through the relevant processing assessments.
Attracting the attention of experts across the globe, Professor of Otology and Neurotology at the University of Sheffield, Jaydip Ray, speculated that:
‘Infrared neuromodulation is a very promising and relatively new concept. If successful on a larger scale, this has the exciting possibility of being a major treatment option for hearing loss’.
Next year, we should be able to revisit this article and reveal whether shooting NIR light into the ear does indeed offer a preventative and/or restorative method for overcoming NIHL.
 Ahmed MM et al., Noise-Induced Hearing Loss Treatment: Systematic Review and Meta-analysis. Military Medicine, usaa579. <https://academic.oup.com/milmed/advance-article-pdf/doi/10.1093/milmed/usaa579/35615111/usaa579.pdf> accessed 13 May 2021.
 Rhee CK et al., Effect of low-level laser treatment on cochlea hair-cell recovery after acute acoustic trauma. J Biomed Opt. 2012 Jun;17(6):068002. <https://www.spiedigitallibrary.org/journalArticle/Download?fullDOI=10.1117%2F1.JBO.17.6.068002> accessed 13 May 2021.
 Roger Dobson, ‘Beaming infrared light into the ear could combat hearing loss by reducing noise exposure, tests show’ (11 May 2021 Daily Mail) <https://www.dailymail.co.uk/health/article-9563879/Beaming-infrared-light-ear-combat-hearing-loss-tests-show.html> accessed 13 May 2021.