Researchers may have narrowed down the reason some people who contract COVID-19 lose their sense of smell and taste.

A new study published in the journal Nature Genetics points to damaged cells in the olfactory epithelium, a part of the nose that traps odor molecules and submits a response to the brain, as the likely culprit.

However, that’s not the end of the mystery.

“Early data suggests that supporting cells of the olfactory epithelium are the ones mostly being infected by the virus, and presumably this leads to the death of the neurons themselves,” Dr. Justin Turner, an associate professor of otolaryngology at Vanderbilt University, told NBC News. “But we don’t really really know why and when that happens, and why it seems to preferentially happen in certain individuals.”

It’s estimated that about 1.6 million people in the U.S. are still experiencing loss of smell and taste more than six months after contracting COVID-19.

Moreover, those who do lose their sense of taste and smell may be genetically predisposed to do so.

Using data from genetic sequencing company 23andMe and cross-referencing it with people who self-reported a positive COVID-19 case, researchers found that people with a tweak to chromosome 4 were more than 10% likelier to experience sense loss.

The researchers hope these new discoveries will enable them to develop treatments to eventually return people’s senses.