A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Is paper money dirty? Plus: Do hand sanitizers cause superbugs?

January 16, 2015

Dear Cecil:

My mother always asked us to wash our hands after touching money whenever possible. But is money really so out-and-out filthy that you risk serious illness every time you hand over cash at a drive-thru and then eat your burger? And: do hundred-dollar bills really have measurable amounts of cocaine on them?

Cecil replies:

[An addition to this column appears at the end]

Get ready for a deluge of I-told-you-so email from vindicated mothers everywhere — in Bangladesh, for instance, where a 2006 study found that about one in eleven paper banknotes tested were contaminated with E. coli or similar bacteria. This isn’t to say that Bangladeshis are literally wiping their butts with money (practically speaking, that’s more likely to happen on Wall Street) but rather that bacteria are everywhere, including on currency. And unlike public toilets, twenties don’t get hosed down every so often.

Lest you think Bangladesh particularly unhygienic, 103 different fungal colonies were found on 60 randomly selected Egyptian banknotes — some of which were producing toxins. Some Philippine currency notes carried the cysts and ova of intestinal parasites, and were subsequently eliminated from use. Topping the list of diseased and potentially hazardous currency is Nigeria, where 90 percent of paper money is a home for bacteria. (Nigerian bills that were retired after heavy circulation proved to be so contaminated they were deemed a risk to treasury workers’ lung function.)

American money might be slightly cleaner. A 2002 study in Ohio that collected and cultured 68 one-dollar bills produced a total of 93 bacterial samples; while 88 of these could pose a threat to people with compromised immune systems, five would be considered dangerous even to the healthy. For context, a similar experiment in Kentucky in 1972 turned up 26 of the scarier bacteria after swabbing 50 low-denomination bills, a rate more than seven times higher — evidence that in some limited ways American life may have become less disgusting over the last 40 years.

And yes, roughly four out of five American bills bear cocaine residue — but only because the powder is so fine that one patient-zero bill in an ATM can easily and quickly spread it to thousands. Don’t get too excited, though: these amounts are so small that no one’s getting high off the U.S. Mint’s supply.

While I’m no more a fan of parasitic cysts than the next guy, let’s reiterate: pretty much everything has germs on it, and most of them won’t kill you. Gas-pump handles, kitchen sinks, your date’s mouth — you name it, it’s probably coated with invisible bugs. Furthermore, we couldn’t find any specific studies that tied illness incidence to handling money. If you’re really paranoid I suppose you could stick to coins, whose copper content seems to suppress their bacteria load. On the other hand, this will limit your cash purchases to gumballs, and may lead to even more awkwardness than usual when visiting strip clubs. Your mom probably warned you against those too, but we’ll keep our noses out it.

Dear Cecil:

I am curious about the use of antibacterial hand gels that are commonly used to disinfect hands. Does excessive use of this substance (say, 40-plus times a day) somehow increase the risk of developing resistant bacteria, much in the same way as prescription of antibiotics has?

Cecil replies:

Heh. One of my little researchers used to deride Purell users as germ wussies. It took one trip to Thailand, three hand-sanitizer-less days and many, many trips to the bathroom before she saw the light. That said, worrying about Purell resistance suggests some possible apples/oranges confusion on your part.

Antibiotics work by disabling certain specific functions of a bacterial cell. For example, penicillin weakens cell walls. Occasionally some rogue bacillus will have some genetic variant rendering its walls penicillin-proof. Usually, your immune system can handle one or two of these guys. But when you take antibiotics needlessly, or incompletely, or off schedule, you may wind up wiping out the nonresistant bacteria and thus selectively breeding the resistant ones, which can then become the main source of infection. A recent example is every college student’s nightmare: a drug-resistant strain of gonorrhea.

Alcoholic hand sanitizers, on the other hand, kill germs by first dissolving their lipid-based outer membranes and then dehydrating the proteins inside. Since nearly all bacteria have lipid membranes, ten-second submersion in alcohol can destroy all sorts of deadly and otherwise unpleasant bugs, from E. coli to staph. (The exceptions are bacterial spores like anthrax, which are basically the cockroaches of the bacterial world: they’ve got extremely thick outer coats and can survive extreme temperatures, chemical damage, and probably nuclear warfare if it came down to it.) For most bacteria, alcohol does such sweeping damage that becoming resistant to it would require a monumental structural leap — it would be like humans developing the ability to breathe without oxygen. It’s not evolutionarily impossible, I guess, but so far the survival rate is zero.

So why don’t we cure tuberculosis with alcohol? You try soaking your lungs in 190-proof ethanol — not only would you die, but they might burst into flame. Cool, perhaps, but ultimately ineffective.

On the (filthy) other hand...

Dear Cecil:

I think your answer to Felix's query about hand sanitizing products was incomplete. While Purell, which you mentioned, is indeed mostly alcohol, many products sold as antibacterial (the word Felix used) contain triclosan and/or triclocarban, which have been implicated in microbial resistance. This is the issue I think Felix may have been alluding to. Even if it wasn't, I fear readers of your answer may not get the nuance of hand sanitizing gel vs. antibacterial soaps and come away thinking Cecil has given his blessing to continue cheerfully contributing to the rise of super bad superbugs. Please consider a follow-up so I can continue rolling my eyes at these germophobes.

Cecil replies:

It’s your lucky day: I will happily condone the teasing of antibacterial soap users everywhere. Not necessarily because they contribute to the strength of superbugs, but because they’re pretty useless. Let me first clarify that all soaps are, to a certain extent, antibacterial — in that they all serve to kick germ butts. However the typical “antibacterial” soaps that most people are familiar with do indeed contain tricloban and triclocarban, which are often used in extremely high concentrations to sterilize surgical implements. Their presence in commercial soaps is a different story: most soaps only contain about 0.2% concentration, and across multiple studies have proven to be no more effective than normal soap. Except for the occasional suspicious soap-company funded trial, the only instances in which tricloban works is in much higher concentrations or when used at least 18 times a day, during hand-washing sessions of at least 30 seconds. No one spends 30 seconds, except brain surgeons and maybe preschool teachers who have to deal with a lot of toddler vomit.

Its contribution to super-bug capabilities, on the other hand, is much more difficult to determine. It is theoretically possible, of course, but unlikely. It would also be very difficult to test — remember, you don’t want to give antibiotics to people who don’t need them. However, we live in a world where the fear of litigation is real — so the FDA has released several warnings to producers just in case.

Other readers have brought up the idea that excessive Purell use can actually be harmful. The answer is no. That’s ridiculous. Alcohol will of course kill some of the “good” or “resident” bacteria along with the germs, but your body easily reproduces these. The amount necessary for it to be harmful would be enormous — just as we mentioned soaking your lungs in alcohol has its issues, so does immersing your hands. If you’re using Purrell to the point that it’s harming you, you probably have some other issues to contend with first.

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