A Gartner analyst at the company's IT security conference in London on Monday raised an unusual problem with some biometric applications.
Research director for the firm Ant Allan said that in some cases the technology is failing to work because people's hands are too clean - just one example of the gap between the way vendors position biometric technology, and its application in the real world.
"It's a cause of frustration in healthcare because staff wash their hands so often the biometric reader cannot scan them," he said. "This could also be applied to people in the office who handle lots of paper."
Allan said that US immigration officials have had to start asking travellers to wipe their fingers behind their ears to put some moisture on their fingers before using fingerprint scanners.
He added that retinal scanners can also be unreliable on people with long eyelashes.
"Don't rely on vendor results," he said. "It's easy to prove [biometrics] lets the right people in, but harder to prove it stops the wrong people."
Overall Allan expressed caution over making too big an initial investment into biometric security kit.
"Be sure that biometrics is right for you. Perhaps a limited rather than a full-scale deployment will be successful," he said.