Persistent loss of smell has left some covid-19 survivors yearning for the scent of their freshly bathed child or a waft of their once-favorite meal. It’s left others inured to the stink of garbage and accidentally drinking spoiled milk. “Anosmia,” as experts call it, is one of long covid’s strangest symptoms — and researchers may be one step closer to figuring it out what causes it and how to fix it.

A small study published online on Wednesday in Science Translational Medicine and led by researchers at Duke University, Harvard and the University of California San Diego offers a theory, and new insight, into lingering smell loss.

Scientists analyzed samples of olfactory epithelial tissue — where smell cells live — from 24 biopsies, nine of which were from post-covid patients struggling with persistent loss of smell. Although the sample was small, the results suggest that the sensory deficit is linked to an ongoing immune attack on cells responsible for smell — which endures even after the virus is gone — and a decline in the number of olfactory nerve cells.