Are bone conduction headphones safer with regards to hearing loss?

Question

In this video, at about 1:35, a claim is made that bone conduction headphones are safer with regards to hearing loss, because the sound doesn't "affect the eardrum".

Is that true? I thought hearing loss is caused by damage to the hair cells in the inner ear, which I'd think can still be provoked by bone hearing headphones if they are turned up very loud.

Answer 1

I wrote about this exact thing in a review of the AfterShokz headphones on my blog. But here's the general idea...

The wording of the AfterShokz marketing material is very clever (from this page). They say:

Scientific studies have found that extended use of regular headphones and earbuds promote hearing loss and damage to the eardrum. Since AfterShokz headphones do not use the eardrums to transmit sound, they provide consumers with a quality stereophonic listening experience while reducing the risk of eardrum damage.

So their wording claims that earbuds promote hearing loss AND damage to the eardrum. The second thing they say is that AfterShokz reduces the risk of eardrum damage. Nowhere do they claim that it reduces the risk of hearing damage!

This web page by the National Institues of Health, has this to say about noise-induced hearing loss:

However, when we are exposed to harmful noise—sounds that are too loud or loud sounds that last a long time—sensitive structures in our inner ear can be damaged, causing noise-induced hearing loss (NIHL). These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back.

And this:

Exposure to harmful sounds causes damage to the hair cells as well as the auditory, or hearing, nerve.

Nowhere on that page does it say anything about eardrums or any connection between eardrum damage and hearing loss.

The conclusions that I take from this are:

1. I ASSUME that damage to the eardrum is mostly from the "stick it in your ear canal" type of earbuds. From physical contact and not from high volume levels from the earbuds. I have absolutely nothing backing this up, except that it fits the rest of what I'm saying.
2. IF #1 is correct then the AfterShokz marketing material is 100% correct (but misleading).
3. The NIH says that hearing loss is caused from nerve damage or damage to the hair cells in your ear. Since both of these are still used by the AfterShokz headphones (otherwise you wouldn't hear anything), it is unlikely that these headphones will prevent hearing loss due to high volume levels.
4. Turning down the volume is still the best way to prevent hearing loss.

Answer 2

From a letter to the editors of Hearing Journal:

The description of the Aftershokz bone-conduction earphones included the statement, “Because the headphones do not use the eardrums to transmit sound, they allow users to listen to music without risk of eardrum damage.” MP3 player earphones are not capable of producing levels great enough to cause an eardrum perforation, so users would not be at risk of eardrum damage from any type of earphone. Rather, listeners are at risk of cochlear damage from overuse of any type of earphone. The fact that these earphones use bone-conduction transducers does not inherently make them any safer than any other earphone, as bone-conducted sound is transduced by the cochlea similarly to air-conducted sound.

Hearing Journal: June 2012 - Volume 65 - Issue 6 - p 4 doi: 10.1097/01.HJ.0000415192.03538.d6 Departments: Letters to the Editor

"Letters: The Truth about Bone-Conduction Earphones" Portnuff, Cory AuD, PhD; Berger, Elliott MS

Answer 3

My understanding (not a doctor) of the consensus on this issue is as follows:

• Neither conventional earbuds nor bone conductors cause eardrum perforation (not loud enough)[0].
• Both conventional earbuds and bone conductors do cause cochlear damage from overuse and high sound levels, since at the point the sound reaches inner ear it doesn’t matter whether it got in by air or by bone[0].

I’d say Shokz is being misleding, and I wish I learned about it before getting bone conductors.

My further speculation (again: not a doctor!) is as follows:

• IEMs with good passive noise isolation (their sleeves generally go into your ear) may be less likely to cause cochlear damage, because the sound reaching your inner ear is quieter overall than with either “shallow” earbuds or bone conductors.
• However, such IEMs or regular earbuds (or earplugs, for that matter) could be liable to cause physical damage to some delicate structures of the middle ear—the damage you can also get from excessively picking your ears with your fingers[1]—and this damage could cause a type of hearing loss that bone conductors do not cause. I also suspect (anecdotal evidence) that IEMs may raise the likelihood of getting infections into your ear, which could also contribute to hearing loss. If true, the chances of all this probably depend on how careful you are with choosing earbud/IEM fit, cleaning and manipulating them.

My personal takeaway: Over-ear or bone conducting headphones may reduce the chance of physical damage from fiddling with your ears. However, they aren’t great in loud surroundings: inner ear damage is caused by overall sound levels, and with bone conductors or other non-isolating headphones your levels are whatever you’re listening to plus external noise.

[0] From The Truth about Bone-Conduction Earphones, quoted also by another answer:

MP3 player earphones are not capable of producing levels great enough to cause an eardrum perforation, so users would not be at risk of eardrum damage from any type of earphone. Rather, listeners are at risk of cochlear damage from overuse of any type of earphone. The fact that these earphones use bone-conduction transducers does not inherently make them any safer than any other earphone, as bone-conducted sound is transduced by the cochlea similarly to air-conducted sound.

[1] From Fracture of the Incus Caused by Digital Manipulation of the Ear Canal and its Diagnosis Using Wideband Acoustic Immittance (emphasis mine):

the first reported case of a fracture of the long process of the incus due to digital manipulation of the ear canal

A finger inserted into the ear canal can produce an air seal, and subsequent quick removal of the finger can result in the fracture of an ossicle. Clinicians should be cognizant of this form of trauma because insertion of a finger, ear plug, and earphone into the ear canal are common. Ossicular fractures can result in high-frequency CHL [conductive hearing loss], and can be misdiagnosed as sensorineural loss because bone conduction thresholds are not measured above 4 kHz. As in this case, an ossicular fracture may be misdiagnosed and result in inappropriate treatment. Here, WAI, a non-invasive measure of ear mechanics, diagnosed a loose ossicular chain.