Loud music and wireless headphones: Beware of 'hidden' hearing loss, here are the signs

Imagine hearing sounds perfectly but not being able to understand conversations in noisy environments. This is what is known as Hidden Hearing Loss, which does not affect the functioning of the ear but the synapses that connect sounds and their comprehension. Millions of people around the world suffer from it, especially the elderly, and a study published in Nature Scientific Reports in January found it in young people who hear loud music. "Anything that is weak, of low intensity, continues to function well, because the fibres carrying low intensity signals are intact," explains Professor Domenico Cuda, president of the Italian Society of Audiology and Phoniatrics. 'Instead, noise, like ageing, mainly targets the synapses of fibres that work at high intensity'. The result is paradoxical: perfect audiometric tests but real difficulties in understanding when the environment becomes complex, such as in a crowded or reverberant hall.

There are two main risk factors: exposure to intense noise and ageing. But it is among young people that new diagnoses are being observed. "We must not be alarmist, but proper attention must be paid to teenagers who use headphones for many hours a day and to musicians," warns the specialist. "Teenagers tend to push the limits with volume and suffer from a certain fragility of these still not fully formed structures." The study of 42 young adults exposed to music festivals with average levels of 100 dBA (A-weighted decibels) documented that, although only one participant showed clinically significant hearing loss, five had acute reductions in electrophysiological markers of synaptic damage, with two cases persisting up to 14 days post-exposure.

The problem is not only concerts. "The intensive use of so-called 'in-ear' headphones, those that are inserted into the ear, can be a problem because, unlike headphones with a cushion that dampens ambient noise and remains further away from the internal structures, it results in a very small residual volume between the vibrating membrane and the tympanic membrane," Cuda points out. 'By a well-known law of physics, if you apply a force to a smaller volume, the resulting pressure will be greater'. This is why experts recommend the '60-60' rule: never more than 60 minutes continuously, never more than 60 per cent of the device's maximum volume. Better still with conventional headphones or those with noise-cancelling systems.

In the elderly, the process is different. "It is the oxidation mechanisms typical of old age that lead to hidden hearing loss," the SIAF president points out. "Lower reparative capacities of oxidative damage, hence lower antioxidant power of the body, cause predominantly damage to these high-intensity fibre ribbon synapses." Studies on human temporal bones show that the loss of synapses with age is almost three times greater than that of hair cells. Research has documented that seven out of eleven subjects over 60 show more than 60 per cent loss of peripheral nerve fibres. "Even if they hear well, even if their hearing is still not too impaired, they still tell you that they have difficulty with understanding words in complex environments and, in addition, they often suffer from tinnitus," the professor confirms.

The warning signs are clear: persistent tinnitus and difficulty understanding words in noisy environments, despite normal audiograms. "When doing the common audiometric examination, the perception of sounds is very good. On the other hand, anything that is supraliminal, that is, that requires volume to be perceived and understood clearly, is disturbed,' says Cuda. This is prompting researchers to improve the diagnostic front by validating electrophysiological markers, while, on the treatment front, some molecules are showing promise even if they are still in the pre-clinical stages. 'Neurotrophin-3 has been shown to regenerate cochlear synapses after acoustic trauma in mice, and overexpression of NT-3 prevents age-related synaptopathies,' the specialist goes on to explain. 'And some substances may be useful tomorrow in a preventive sense. In the meantime, hearing protection and limiting exposure remains the only accessible strategy.