Because the COVID virus and Long COVID is still relatively new, we are not completely clear yet on how or why the COVID virus causes the loss of smell or abnormal smell/taste. Unlike similar colds, this change or loss of smell doesn’t occur because of nasal congestion or stuffy nose. Recent findings suggest that this occurs because of a dysregulation of the autonomic nervous system (ANS). This COVID virus can also lead to nerve damage to the nasal receptors of the olfactory bulb near the brain. It is not clear why this persists after repair of the nerves. Impaired cerebral blood flow is another reason from dysautonomia or just dysregulation. Most of the time, these symptoms are self-limited to several weeks or several months. Occasionally, these symptoms can continue to persist for a year or longer.
Often, anosmia that occurred during the acute phase of the covid infection will turn into parosmia later on.
Stellate ganglion block has been the most successful so far for smell and taste restoration both for parosmia/dysgeusia and anosmia/ageusia. Other treatments that have worked have been:
None of these are effective for every single person suffering from smell and taste disturbances.
In general, smell training has not been effective in restoring smell and taste. There has been some limited success from stem cell injections into the olfactory cleft area, but the studies were not specific on the amount of recovery.