A 62-year-old man from Singapore was traveling to the U.S. to see relatives last December and was detained after a routine fingerprint scan showed that he actually had none. So how did this happen?



The man, identified in a medical journal case report only as "Mr. S," had been on chemotherapy to keep his head and neck cancer in check. As it turns out, the drug, capecitabine (brand name, Xeloda) had given him a moderate case of something known as hand–foot syndrome (aka chemotherapy-induced acral erythema), which can cause swelling, pain and peeling on the palms and soles of the feet—and apparently, loss of fingerprints.



Mr. S's doctor, Eng-Huat Tan, a senior oncology consultant at the National Cancer Center in Singapore, described the incident in a letter published earlier this week in Annals of Oncology and recommended patients on that drug obtain letters from their doctors before traveling to the U.S.



Officials allowed Mr. S to enter the country following a few hours' detainment when they were "satisfied that he was not a security threat," Tan noted in his letter. Mr. S says he had not noticed that his fingerprints had vanished before he set out on his trip, and his doctor found informal online mentions of other chemo patients complaining of lost fingerprints.



Forensics expert Edward Richards, director of the Program in Law, Science and Public Health at Louisiana State University, explains that "other diseases, rashes and the like can cause vesicular breakdown of the skin on your fingers—just a good case of poison ivy would do it." But, he notes, "Left alone, your skin replaces at a fairly good rate, so unless you've done permanent damage to the tissue, it will regenerate."



As fingerprint scanning and other biometrics become more common (visitors seeking entry into the U.S. must have their prints scanned to ensure they do not currently hold a visa under another name), scanning technology is also advancing. But cases such as this point out that you actually need fingerprints for identification. So how effective are current scanners, and how else have people—accidentally or intentionally—altered their fingerprints?



To find out, we spoke with fingerprint expert Kasey Wertheim, president of Complete Consultants Worldwide, LLC, which provides fingerprint examination expertise to government clients and has done forensic and biometric work for the U.S. Department of Defense and Lockheed Martin.



[An edited transcript of the interview follows.]



Are all fingerprints truly unique?

Yes. It has to do with how the fingerprints form in the womb. During the first trimester, the fingerprints have already established their permanence and uniqueness.



Aside from forensics and travel, what else are fingerprint scans being used for these days?

More and more, fingerprints are being used in biometric devices to permit secure log-on, to open locks, and for access control in general. The biggest users of biometrics are corporate and private users, but fingerprints also have a long history in the forensics world for criminal identification dating back over a century.



Are current scanners pretty reliable?

The exact rate of print rejection [those that can't be read] depends on the scanner. Ultrasound devices go beyond just the outer layer and capture part of the root system. On average, the rejection rate for [scanned] fingerprints is about 1 to 2 percent.



The patient who was detained for lacking prints had hand–foot syndrome that was caused by his chemotherapy drug. What are some other ways that fingerprints can disappear?

The most prominent of those problems involve bricklayers—who wear down ridges on their prints handling heavy, rough materials frequently—or people who work with lime [calcium oxide], because it's really basic and dissolves the top layers of the skin. The fingerprints tend to grow back over time. And, surprisingly, secretaries, because they deal with paper all day. The constant handling of paper tends to wear down the ridge detail.



Also, the elasticity of skin decreases with age, so a lot of senior citizens have prints that are difficult to capture. The ridges get thicker; the height between the top of the ridge and the bottom of the furrow gets narrow, so there's less prominence. So if there's any pressure at all [on the scanner], the print just tends to smear.



How have people intentionally changed or "disappeared" their fingerprints?

There are many documented cases of intentional fingerprint mutilation, but generally those involve pretty severe damage to the skin—more specifically between the generating layer, where the template of the fingerprint survives, and the upper layer, the epidermis.



Pretty much any cut or burn that goes deeper than the outer layer of the skin can affect the fingerprint pattern in a permanent way. But even with permanent scarring, the new scar becomes a unique aspect of that person's fingerprint.



The first case of documented fingerprint mutilation was in 1934, by Theodore "Handsome Jack" Klutis, who led a gang called the College Kidnappers. When the police finally caught up with him, Klutis went for his gun and the police returned fire, killing him. When they compared his postmortem fingerprints, police found that each of his prints had been cut by a knife, resulting in semicircular scars around each fingerprint. Although it was glorified in the media, it was an amateur job; the procedure left more than enough ridge detail to identify him.