SCANNING MYSTERY: Trying to fool a scanner technician with disguised prints would be difficult, Richards says, but what happens if a person doesn't have any fingerprints to begin with?
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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.]