Smell loss after COVID19 Infection Affects Both Taste and Smell Function
Most reports of sensory loss after COVID19 infection have mentioned smell loss. However, reports of taste loss have also been noted by many patients.
The taste loss has been called ageusia by most clinicians, when really it is a hypogeusia, similar to its associated hyposmia.
The important concept here is the similarity in mechanisms underlying both taste and smell loss. The loss is not neural in origin, but involves the biochemical bases for taste as well as smell loss.
Taste buds turn over rapidly, on a daily basis. They depend upon a stem cell which is stimulated by specific growth factors present in saliva. Following a COVID19 infection, several of the clinical moieties in saliva are inhibited by the viral RNA, which inhibits the secretion of these growth factors and inhibits action of these growth factors on taste bud stem cells, thereby inhibiting growth and development of taste bud receptors and subsequent loss of taste. The taste loss can be simultaneous with smell loss which relates to similar loss of smell receptors and subsequent loss of smell.
The biochemical mechanisms responsible for these sensory changes are similar for both sensory modalities.