Having trouble unlocking your phone? You may have lost your fingerprint.

Terri Krejci, 60, of Huntsville, Alabama, was working as a night shift manager at CVS in 2014 when she found out she had breast cancer. She underwent six months of chemotherapy, followed by surgery. Her medical team warned her that she might lose her hair, that she would feel nauseous. She had no idea that she might lose her fingerprints.

“It was right after my second round of chemo, and I had a Samsung phone with Touch ID, and it kept saying ‘fingerprints not detected,’” said Krejci, now retired. “Then one of the nurses said, ‘Oh yeah, I guess we forgot to tell you about that. That happens.’ They said it might be a while before I saw those fingerprints again.”

This caused a particular problem—Krejci needed to use her fingerprint ID to get into the oncology ward. Each time, someone had to let her in, until they finally gave up and gave her a code. Ten years later, her hand is mostly back to normal, she says, but she still has to regularly reset the fingerprint scanner on her phone.

Langenburg, the forensic scientist, says fingerprint problems aren’t going away anytime soon. He predicts a trend toward using multiple biometrics to compensate for potential fingerprint problems—retina scans or facial recognition. And such as fingerprints.

For people who know they have fingerprint problems—construction workers, rock climbers—there are ways to make your prints easier to read, he says. Make sure you stay hydrated and use hand sanitizer or lotion right before scanning. In Minnesota and Wisconsin, fingerprint experts use “breast ointment”, is often used on cows, as it makes the fingers a little sticky and that helps to record fingerprints.

Of course, there are some people want their fingerprints are obscured—especially criminals. “They will often pay a lot of money to try to hide their fingerprints through acid or surgery or whatever,” he says. Thomas Buseya professor of psychological and brain sciences at Indiana University who studies the use of fingerprints and accuracy of fingerprint analysis.

But Langenburg said going through such complicated procedures often has the opposite effect, creating a more unique mark. He pointed to the American gangster John Dillingerwho cut off his fingers and then poured acid on them, scarring the middle of the fingers but leaving all the fingertips, joints, and edges of the fingers identifiable. “As soon as we see red flags like that, we know right away that this person is trying to hide their identity. It’s a ridiculous thing that’s been going on for 100 years and it’s not working,” Langenburg said.

Busey believes it’s odd that we’ve ended up focusing on fingerprints for biometric identification. Criminal fingerprints typically include a scan of all 10 fingers as well as the palm, capturing a huge amount of detail, whereas something like a phone or a computer or an airport scanner might use just one finger or just a region of that finger. It’s a very limited identifier if something goes wrong—and one that can spread.

“You may have a password to your computer, and you may not be in the habit of sharing your password with other people,” Busey said. “But when your fingerprint is your password, you’re essentially leaving your password on every object you touch.”