Crime doesn't pay—except for when it does. The best way to make sure crime does pay is to not get caught, and a good way to not get caught is to not leave evidence. Dexter, the fictional TV serial killer, always wears gloves to make sure that the crime scenes, like the detectives, remain clueless. Yet thanks to a recent study, we now know Dexter might be able to render his fingerprints unreadable by practicing his knife skills on bags of onions.

It's not that the fumes coming off the odoriferous bulbs somehow dissolve the ridges that have left many a burglar clutching prison bars instead of booty. No, the effect that might make a perpetrator walk is more pedestrian. The research, published online last December in JAMA Dermatology, found that anyone suffering contact dermatitis of the hands has a decent shot at owning unreadable fingerprints. And a good way to contract contact dermatitis is to slice onions until you're blue in the face and red in the digits.

The study included 100 volunteers with hands delicate and creamy (think of George Costanza's before the unfortunate incident with the hot iron) and 100 subjects with thumbs affected by dermatitis. Twenty-seven of the dermatologically challenged participants were unable to produce a readable fingerprint for a scanner, compared with only two of the control group. Should print evidence be required, therefore, about a quarter of indicted hand dermatitis sufferers could presumably wave their dry, cracked hands to courthouse reporters after acquittal.

Numerous other methods exist besides ratatouille preparation for turning one's whorls into wheals. An efficacious strategy is unusually frequent hand washing, which doctors should nonetheless do and which hypochondriacs should see a doctor about. Playing with poison ivy, oak or sumac can also work. Some people react to touching latex—yes, in one of the universe's lesser ironies, wearing rubber gloves to conceal your fingerprints can cause a skin reaction that degrades your fingerprints.

Of course, the study was performed not to elucidate ways by which criminals' hands can help them avoid the long arm of the law. The real purpose was to determine if a lot of people might have problems with increasingly common biometric identification systems. If a thumb scanner must identify your print before you can enter your workplace, a skin condition could leave you out in the cold, perhaps literally, which is only going to make that chapped finger even less readable.

Nevertheless, truly enterprising criminals who read JAMA Dermatology might consider fingerprint defilement to be a worthwhile strategy. That subset of the population almost certainly does not include one Florida man, who recently made a name for himself in the annals of duh.

Actually he already had a great name for someone in his line of work. According to the Daytona Beach News-Journal, 19-year-old Matthew Dollarhide was discussing a drug deal when he unknowingly butt dialed 911, thereby allowing emergency dispatchers to overhear and record his conversation.

To the uninitiated, the always helpful Web site Urban Dictionary includes a definition that describes “butt dial” as “accidentally dialing a cell phone that's in your pocket,” presumably by sitting on it in just the right/wrong way and probably by hitting the redial button, “and the resulting broadcasting of a conversation.” Urban Dictionary's current example of usage is: “We heard all the personal details of his blind date after he butt dialed the apartment landline,” but look for Mr. Dollarhide to become the new exemplar.

Authorities tracked the location of the call as they overheard these tantalizing clues: the butt dialer noted that he was driving a tow truck and (like Dexter) frequently mentioned “Harry.” According to the news report, “that made it easy for deputies to spot the white tow truck with ‘Harry's Towing’ written on the side.” It's doubtful that the officers will have trouble showing that they had probable cause for the ensuing stop. And it's likely that fingerprint evidence will not be required.

SCIENTIFIC AMERICAN ONLINE
Comment on this article at ScientificAmerican.com/apr2013

This article was originally published with the title Show Your Hand.

4 Comments

1. 1. bucketofsquid 06:27 PM 4/12/13

   Considering that previous research showed that finger print "experts" had only about a 5% success rate identifying the same person by their finger prints twice in a row, which yields a 95% failure rate, I wouldn't worry about it much.

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2. 2. rigg38a 02:54 AM 4/13/13

   I once built a double wall of purbeck stone and made the mistake of distributing the cement around the pieces in the inner wall cavity with both hands. I had most of my fingers covered in magnesium sulphate and bandages for over a week to remove the ingress of cement - painful too. Could I have flown into the USA during this time? What happens at an airport if your fingerprints are unreadable for any reason?

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3. 3. bluesdoc 05:37 PM 4/15/13

   I bought a biosensing (fingerprint reader) lock mechanism about two years ago that came highly recommended. I could not get it to work for me. Many emails and phone calls later, I came to learn from the head tech guy that 'yeah, these don't work well for physicians - too much hand washing reduces fingerprint ridges'. Great...

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4. 4. kcchant 01:29 PM 4/25/13

   After retiring from a 35 year teaching career, in the process of being rehired as a substitute teacher, it was necessary for me to be fingerprinted. I was fingerprinted at a nearby state police office, but the State Education Department notified my school district that the prints were unreadable. I returned and submitted a second set of prints. Same result. I decided to try the local police station convinced that the third time would be the charm! Not so. I received a fingerprint clearance that limited my employment to the district where I previously worked which is all I needed. But I have no idea why my fingerprints are unreadable!

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