Does sharing earphones increase the risk of middle ear infections?

Question

A Google search reveals many claims that sharing earphones is unhealthy.

Marie Claire magazine provides an example:

Kelly Reynolds, Ph.D., associate professor of environmental health at the University of Arizona also told Buzzfeed US that 'studies have shown that earbuds cause an 11-fold increase in bacteria in the ears' and 'when you share headphones, you’re doubling the microbial flora in your ears and introducing new bacteria'. [...]

Bad earphone hygiene can also cause a whole host of nasty ailments too: Middle ear infections, fungus, swimmer's ear, blackheads, pimples to name a few. And Reynolds noted that because our wax also contains strep bacteria, if we have a cut or open wound near to the wax, it could also cause a serious skin infection.

I'm failing to find any scientific studies regarding this matter.

Picking one claim, does sharing earphones increase the risk of middle ear infections?

Answer 1

It seems reasonable that earphone use would increase bacterial growth, because covering the ear would provide reduced airflow, increased humidity, and limited light, which are favorable conditions for bacteria. I've found a publication related to this issue, although it does not come from a journal with a high impact factor. (Actually, I couldn't find its impact factor.) The article concludes that earphones can cause increases in bacteria with regular use, and they suggest that sharing earphones is a potential disease vector.

Frequent and constant use of earphones increases the bacterial growth in the ear and sharing of earphones might be a potential vector of commensals.

From A Comparative Analysis of Bacterial Growth with Earphone Use.

If we can accept the notion that using earphones can increase levels of bacteria present in the ear, then sharing earphones certainly seems like a feasible method of transferring some of those bacteria. In fact, even if we assume that earphone use doesn't increase levels of bacteria, sharing earphones could still be a potential disease vector, as there could still be transmission of the bacteria that are normally present in the ear, some of which could cause infection.

As a further note, I found another study looking at ear infection and hearing problems among customer service reps at a specific company. However, the experiment had no control group, and the inferences and conclusions leave much to be desired. I'm somewhat suspicious that the research may have been funded by the company, as the only emphasized outcome is that they found no association between hearing loss and headphone use. I will share the link to disclose what I have found, but I certainly don't endorse the source: Ear Infection and Hearing Loss Amongst Headphone Users