Getting an ultrasound of the thyroid if you have no symptoms doesn’t seem to help people live longer or prevent them from dying of thyroid cancer, according to a study in Korea.

In South Korea, more people were diagnosed with thyroid cancer between 1993 and 2011—not because more people were getting sick, but because doctors started using ultrasound scans to check everyone’s necks, even if they felt fine, and found lots of tiny, harmless tumors that would never have caused problems.

In 2015, South Korea decided not to routinely scan healthy people’s necks with ultrasound to check for thyroid cancer, because they thought it wasn’t helpful for most people.

In South Korea, more people are being told they have thyroid cancer than before, but not fewer people are dying from it — which means many of those new diagnoses might be for cancers that wouldn’t have hurt them anyway.

In South Korea, more and more people started finding thyroid cancer through routine scans between 1999 and 2008 — and this happened right after doctors began using ultrasound machines much more often thanks to new health rules.

More people were diagnosed with thyroid cancer between 1999 and 2008, and most of that increase came from ultrasounds finding tiny, harmless lumps in the thyroid—so it’s not that more people got sick, but that we’re just finding tiny things we wouldn’t have noticed before.