The silent epidemic of permanent hearing loss
We started to evolve as humans around five million years ago, with hearing to enable us to communicate and keep us safe. Our hearing hasn’t evolved much since and has not caught up with the technological advances of reproduced sound through amplifiers and loudspeakers.
We use headphones more and more in our daily lives, but our hearing has not evolved to be exposed to these large sound doses and, according to the World Health Organisation (WHO), as a result more than 2.5 billion of us are at risk of permanent, avoidable noise induced hearing loss by 2050.
The biggest source of large sound doses for most of us is from headphones, so new safety standards have been introduced to provide us with information about our sound exposure over time so we can manage it ourselves.
Our ears are an amazing part of the body that help deliver the vital sense of hearing, but they are fragile and easily damaged. Repeated exposure to high sound doses through the use of headphones and earbuds can permanently damage hearing in a way that cannot be recovered.
Until evolution catches up, we need to adapt to this recent increase in sound dose and be aware of our exposure, so we can make informed decisions about our listening and protect our hearing.
We can hear sound because of vibrations (sound waves) that enter our ears that we then decipher. The outer ear directs sound waves into the ear canal where they travel to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear that amplify the sound vibrations and send them to the inner ear. The inner ear contains a structure filled with fluid called the cochlea. Sound vibrations create waves in the cochlear fluids. As the waves peak, they cause tiny hair cells within the cochlea to bend, which convert the vibrations into electrical signals interpreted by the brain through the auditory nerve.
At birth, humans have about 15,000 auditory hair cells within the cochlea of each ear. These cells are the critical point where the physical noise energy is converted to allow your brain to detect and interpret the sound, with different hair cells able to respond to different ranges of sound frequencies. These hair cells are very vulnerable to irreparable damage by regular, repeated exposure the large sound doses and excessive noise. You don’t get any more and when they are gone they are gone - and so is your hearing. By the time you notice hearing loss, many hair cells have already been destroyed and cannot be repaired or replaced, and worse still this damage can take a long time to show up.
Because we tend to lose the outer hair cells through cochlea damage first, early hearing loss presents itself as a diminished ability to distinguish sound frequencies and therefore the quality of speech or music; we struggle to distinguish and understand speech, particularly when there is background noise. Eventually, if hearing loss continues, it can become hard to understand speech even in quieter places. In addition to damaging hair cells, repeated exposure to high sound doses can also damage the auditory nerve that carries information about sounds to your brain.
The solution to minimise hearing damage from the use of headphone products is to understand the degree to which your ears have been exposed to potentially damaging sound energy, and make sensible, informed choices about how to listen in order to stay within safe limits. The challenge is that the measurement of the sound energy exposure over time is not a trivial matter and certainly not something that can be intuitively gauged: it is a complex combination of listening period (time), how loud you listen (volume) and the energy content (density) of the sound you listen to.