Loss of smell was added to the UK government's official list of symptoms for COVID-19 in May 2020.
Some people who lost their sense of smell after testing positive for coronavirus have said it still hadn't returned six months after becoming infected.
The precise cause of this sensory loss related to coronavirus is not known, but scientists believe it is caused by damage to infected cells in part of the nose called the olfactory epithelium - which is found in the nasal cavity.
These cells protect olfactory neurons, which help humans smell.
A genetic locus, meaning the specific location of a gene on a chromosome, near two olfactory genes is associated with COVID-induced loss of smell and taste, according to a study published in the Nature Genetics journal.
This genetic risk factor increases the likelihood a person infected with COVID will experience a loss of smell or taste by 11%, the study says.
