Does wearing headphones increase bacteria in the ear? Do refrigerators promote cold-resistant bacteria?

December 28, 2007

Dear Cecil:

Here's one that's making the rounds: "Wearing headphones for just an hour will increase the bacteria in your ears by 700 times." What's the dope? -- Paul Spadoni

If antibiotics, antibacterial soap, and chlorinated water all help create bacteria resistant to such things, what about refrigerators promoting cold-resistant bacteria?

Though it's got the classic ring of an urban legend, Paul, the statistic you cite is fairly accurate up through "ears," after which it goes awry. The problems are (1) the rumored scale of the phenomenon is way off and (2) the stat may not tell us too much, besides that ears are livelier places than one might imagine.

The source of this idea seems to be a 1992 study from the medical journal Laryngoscope in which Itzhak Brook and William Jackson measured bacteria levels found on 20 audio headsets of the type provided on commercial airline flights. At the beginning of the experiment, the typical headset had 60 microorganisms on its surface; after an hour's use of the headphones by a volunteer, that number went up to 650 - roughly 11, not 700, times more. This could suggest that headphones make germs procreate like crazy, an icky enough image, but the authors say it's more likely that the heat and humidity created in the user's ears cause "resident organisms from the deeper skin layers and the sweat and sebaceous glands" to congregate out in the open, which to some might seem far ickier.

So we've got the general idea that headphone use for an hour = lots more bacteria, but where did that 700-times thing come from? Here we turn to the "Practical Traveler" column in the New York Times of January 3, 1993. Addressing the topic of germs lingering on airplane pillows, headrest covers, and headsets, writer Betsy Wade summarizes the Brook and Jackson report as saying their "research showed a 100- to 700-fold increase in bacteria" on the headset. Now, the Straight Dope staffers and I have turned that study upside down and can't fathom how Wade got her numbers. Whether they arose from a cryptic reading of the data, a misreading, or a proofreader's slip, it's of such that Internet factoids are born.

The bigger question is: fine, wearing headphones causes the ears to teem with bacteria; other than grossing us out, does this affect our lives? Unclear. Though they warn of potential risk, Brook and Jackson couldn't tie the germ increase to actual health trouble; a Malaysian study of 118 phone-support workers who used headsets seven hours a day found that 11 had chronic ear, nose, and throat problems, but in only four cases were those were related to ear infections. Other ear research suggests that pretty much anything you stick in there - stethoscopes, hearing aids, audiological gear - comes out covered in microbes, but those microbes don't necessarily make anyone particularly sick. So unless you're prone to getting ear infections - or you're one of those germ freaks we all know and love - the headphones-bacteria effect may be more curiosity than wake-up call.

Now, Anna: If you'd thought about it for perhaps ten seconds before hitting "send," you'd have recalled that there are several natural phenomena - one of the best-known is called winter - that produce refrigeratorlike conditions without any human help. So bacteria have had quite a bit of experience dealing with cold: many land-dwelling varieties do some of their best work at fairly low temperatures; others have developed enzymes allowing them to subsist in frigid deep-sea water. (Larger parasitic creatures have evolved for chilly weather, too - there's an arctic variety of the trichinosis roundworm that turns up in walrus and bear meat. Before anyone asks, no, there's currently no evidence that eating woolly mammoth puts you at risk.)

In some situations, cold-resistant bacteria are considered a plus. They're often used in water treatment and gardening, and researchers have tried to breed strains of bifidobacteria, a type of beneficial digestive flora, that can flourish in refrigerated dairy products.

I'll concede that in 2003 the Lancet did run a paper proposing a "cold-chain hypothesis" linking refrigeration, bacteria, and the chronic inflammation of the bowel called Crohn's disease. Boiled down, the idea is that (a) cold-resistant bacteria may be responsible for Crohn's and (b) an increase in Crohn's diagnoses in certain world regions during the 20th century correlate roughly with the advent of widespread refrigeration. As of now, though, any apparent connection seems to be mainly a bunch of interesting coincidences, and the authors concede that even if they're right there'd clearly be no overall benefit in abandoning the refrigeration of food. It may be tough to remember at this time of year, but the humble household fridge is one of the more useful devices going - beyond keeping those cold ones cold, it's put a historic dent in food poisoning incidence throughout much of the planet. A refrigerator-borne disease would have to be Ebola-style horrific to make the trade-off look like a raw deal.

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