Dr Robert MacKinnon, a clinical scientist with a PhD in otorhinolaryngology, discusses the importance of protecting our ears from noise damage.
He explains how the auditory system works, the risks posed by excessive noise exposure and practical tips on preserving hearing health.
Be they petite and demure, or grand enough to make Yoda blush, we are each typically born with a pair of ears, and, invariably, they have to last us a lifetime. It is prudent to take care of them because, as Evander Holyfield can attest, we don’t grow new ones if they are damaged (even 31 years later)!
Thankfully, the thing most likely to take a bite out of our hearing is the amount and type of noise we expose our ears to. To that end, this article will explain a bit about how the human auditory system functions, the impact of loud noise, and provide some guidance on protecting our ears so that they last a lifetime.
The Ear
We have evolved a very effective auditory system, focused on a pair of vibration detectors in the form of our ears. It is a system able to convey a huge range of sound intensities, from the barely perceptible rustling of leaves to a jet taking off at full throttle.
Image – Edited from Perception Space —The Final Frontier, A PLoS Biology Vol. 3, No. 4, e137 doi:10.1371/journal.pbio.0030137 – Creative Commons 2.5 License
The human ear has three parts:
- The outer ear: This is the visible part of the ear on the side of the head (called the pinna) and the external ear canal (or auditory canal) that goes inside the head, ending at the eardrum (tympanic membrane). This part of the ear channels sound vibrations into the ear and onto the eardrum, and gives a boost to the frequencies most important for speech.
- The middle ear: This is composed of the eardrum and the three smallest bones in the human body (called the hammer or malleus, the anvil or incus and the stirrup or stapes), which are held in an air-filled space in the head (the tympanic cavity). The middle ear helps to boost the vibrations at the eardrum into stronger vibrations that can be better detected by the inner ear. The stapedial reflex causes one of the ligaments in the middle ear to tense, which helps reduce the intensity of very loud sound. You might have heard this kick in, for example, when holding a crying baby or when a fire alarm goes off!
- The inner ear: The hearing part of the inner ear is called the cochlea. This is a fluid-filled spiral structure that is pushed on by the stirrup or stapes of the middle ear. The vibrations that are delivered to it are turned into electrical signals by specialised cells called hair cells. There are two types: outer hair cells, which give gentler vibrations a boost and some tuning, and inner hair cells, which then take those vibrations and, through the displacement of their tiny “hairs” (cilia), generate the nerve impulses that go to the brain. These electrical signals are then sent along the cochlear nerve to the brain. However, if sounds are very loud, these hair cells can be overwhelmed and may end up permanently damaged. Both types can be damaged by loud noise exposure, and that damage is, so far, irreversible. This can occur by a single loud sound or by repeated exposure to loud sounds. We will call these sounds collectively noise.
Noise
When sounds reach a certain intensity, they can potentially damage our hearing as loud noise. Such noise can be unwanted (for example, noise from loud machinery at work) or it could be desired (like listening to music with the volume turned up). It is important to identify which noise can be damaging to hearing, and how to go about reducing the risk of damage. To this end, understanding noise as something with a “dosage” is helpful.
The dosage of noise we expose our ears to depends on two things – the intensity and the duration of the sound. Understanding these will give us the tools to help protect our ears from excessive noise.
Intensity: We talk about sound intensity using the decibel scale (dB), which relates the intensity of sound to the quietest sound we can hear. It is a logarithmic unit, where an increase of 3dB equates to a doubling of sound energy and intensity – so an 88dB sound is twice as intense as an 85dB sound. It’s not something we can easily measure without equipment (be careful with apps on your phone as they’re often not accurate!), but if you have to shout to be heard by someone two metres away (the so-called “SHOUT!” test from industry), the sound is likely loud enough to be a potential risk [1]. We take a specific type of dB as our loudness measure, dB(A), which takes into account the sensitivity of human hearing at different frequencies [2].
Duration: This is much easier for us to determine. For context, from occupational noise exposure guides, it is considered reasonable to be exposed to an 85dB(A) sound for eight hours a day, five days a week. We can use what we know about levels to then translate this to other sound intensities, with each 3dB increase halving the acceptable exposure time. An 88dB(A) sound would thus be acceptable for four hours, and a 91dB(A) sound for two hours.
Applying this to occupational exposure in a work context, an eight-hour working day is the baseline duration expected to give a 40-hour working week. The intensity is the expected average level (in dB(A)) over a day or that week. The UK Health and Safety Executive [3] requires employers to:
- At 80dB(A) – Assess risk to worker health and provide information and training.
- At 85dB(A) – Provide hearing protection and hearing protection zones.
- At 87dB(A) – This is the exposure limit when taking into account hearing protection. Workers must not be exposed above this level.
However, there are also exposures outside of work too – so-called recreational exposure comes in a variety of forms, such as listening to loud music, and noisy hobbies like DIY, motorcycling and shooting. These are less likely to be monitored as accurately as workplace exposures, but the SHOUT! test could still be useful. Being mindful of such exposure adding to dosage on top of that in the workplace is also important for our hearing health.
One area of cross-over is live or amplified music, which can be a noise source in an occupational context (and thus covered by HSE regulation) or as a concert-goer. As public rather than professional guidance, the UK Health and Safety Executive recommends that sound intensity does not exceed 107dB(A) over the event, anywhere in the audience area [4]. This would be a level “safe” to listen at for around two to three minutes. Event organisers are also advised to give public warnings if levels are expected to exceed 96dB(A) [4]. Assuming this level is met, this gives a “safe” duration of around 30 minutes to one hour.
Consequences of noise exposure
Exposure to loud noise can have consequences for your ears, the most obvious of which is hearing loss. If noise is the suspected cause, this is termed noise-induced hearing loss. As mentioned above, exposure to loud noise can damage the hair cells in your cochlea, resulting in hearing loss at certain frequencies.
This hearing loss can be temporary and recover within a day or two, or permanent, and not recover at all. Even if the hearing loss is temporary, it should be taken as a warning that permanent damage is likely if exposure continues. Such hearing loss makes it harder to hear the quieter sounds encountered in daily life and can make it harder to understand speech, particularly in background noise. There is also evidence that noise exposure can damage the nerve fibres that go from the cochlea to the brain, and that this damage doesn’t necessarily show up in hearing tests such as an audiogram [5].
In addition to hearing loss, there are other risks from loud noise exposure. Loud noise exposure can sometimes cause a ringing or buzzing in the ears called tinnitus. Sometimes tinnitus goes away after a few minutes or hours after a loud noise exposure. However, sometimes it can persist for weeks, years, or even indefinitely, especially if you have a noise-induced hearing loss. This can have significant consequences and a big impact on quality of life.
So with the potential risk posed, especially with repeated exposure, what can you do to care for your ears?
Preventing noise damage
- Minimising exposure and regular breaks
The best solution is to minimise time in noisy environments altogether. Avoiding noisy situations outright is, of course, not always practical but does immediately cut dosage. Where noise is unavoidable, it’s sensible to take a break from the noise and rest your ears, giving them periodic relief. There is no hard and fast rule for how long or how often, but if your hearing feels dulled or you hear any ringing or other noises afterwards (tinnitus), it’s a good indicator that you may have overwhelmed your ears, so a break sooner next time might be a good idea.
2. Ear protection
This can be sensible, especially in the context of DIY or live music listening. Protection ranges from universal foam earplugs (sometimes buried in the toolbox for years past or handed out at events designed for industrial noise -please use fresh and clean ones!), to plugs with a “flatter” response across low and high-pitched sounds to keep music sounding more natural, through to custom-fitted plugs for musicians and the type that enclose the ear completely (so-called “circum-aural”). It’s worth exploring options with a couple of things in mind:
1 – They needn’t be hugely strong in attenuation. Remember, just a 3dB drop in intensity doubles exposure time. So, assuming a 94dB(A) average level, 3dB plugs would extend “safe” listening time to two hours and 6dB to four hours.
2 – A legitimate commercial product will be far more effective than traditional “cotton wool” or other improvised plugs. These aren’t effective at blocking noise and, at worst, could mean a trip to the audiologist or GP!
Hearing protection is particularly important for children, who evidence shows may have a lower threshold for “safe” exposure [6]. It’s recommended they use hearing protection (probably circum-aural, for better protection and to avoid choking hazards) irrespective of the duration of any exposure [7].
3. Distance
Sound waves obey the inverse square law, meaning if you double your distance from the source (speaker, equipment), the intensity drops four times (so 6dB), thus quadrupling safe listening time. If you feel that you’ve given your ears a bit of a hammering, moving away from the source can have a big effect on your exposure.
4. Use common sense
Take general care of yourself and ensure you drink and eat enough, but particularly with alcohol, not too much. We have some evidence (both in the literature and anecdotally) that alcohol consumption makes our ears less sensitive to sound (though still able to be damaged by it) [8], meaning we may be less aware of how loud a sound is, and less likely to move away or take a break as needed. Additionally, there is some evidence that alcohol consumption may make us more susceptible to noise damage itself, particularly if we have a flushing reaction when drinking alcohol [9].
Summary
In short, the old adage “everything in moderation” remains valid here. A balance of minimising exposure and enjoying things like music, while taking sensible precautions, will help you enjoy your hearing for years to come. You’ve only got one pair of ears – let’s treat them accordingly.
Dr Robert MacKinnon Clinical Scientist and Deputy Head of School Anglia Ruskin University Cambridge, UK
References:
[1] https://press.hse.gov.uk/2023/10/16/try-the-shout-test-protect-workers-hearing/
[2] ISO 1996-1:2016(en) Acoustics — Description, measurement and assessment of environmental noise — Part 1: Basic quantities and assessment procedures
[3] https://www.hse.gov.uk/noise/regulations.htm
[4] https://www.hse.gov.uk/event-safety/noise.htm
[5] Stone, M. A., Perugia, E., Bakay, W., Lough, M., Whiston, H., & Plack, C. J. (2022). Threshold equalizing noise test reveals suprathreshold loss of hearing function, even in the “normal” audiogram range. Ear and hearing, 43(4), 1208-1221.
[6] Roberts B, Neitzel RL. Noise exposure limit for children in recreational settings: Review of available evidence. J Acoust Soc Am. 2019 Nov;146(5):3922. doi: 10.1121/1.5132540. PMID: 31795717.
[7] Sophie J. Balk, Risa E. Bochner, Mahindra A. Ramdhanie, Brian K. Reilly, COUNCIL ON ENVIRONMENTAL HEALTH AND CLIMATE CHANGE, SECTION ON OTOLARYNGOLOGY–HEAD AND NECK SURGERY; Preventing Excessive Noise Exposure in Infants, Children, and Adolescents. Pediatrics November 2023; 152 (5): e2023063752. 10.1542/peds.2023-063752
[8] Upile T, Sipaul F, Jerjes W, Singh S, Nouraei SA, El Maaytah M, Andrews P, Graham J, Hopper C, Wright A. The acute effects of alcohol on auditory thresholds. BMC Ear Nose Throat Disord. 2007 Sep 18;7:4. doi: 10.1186/1472-6815-7-4. PMID: 17877829; PMCID: PMC2031886. [9] Lee J, Jeong Y, Kim J, Kwon S, Seo E, Jeong J, Lee W. The impact of alcohol consumption on hearing loss in male workers with a focus on alcohol flushing reaction: the Kangbuk Samsung Cohort Study. Ann Occup Environ Med. 2024 Jan;36(1):e1. https://doi.org/10.35371/aoem.2024.36.e1