The vast majority of patients who complain of a disorder of taste actually have a disorder of smell. We are only capable of tasting four things (salt, sweet, sour and bitter). There are four nerves that carry taste sensation and it is very rare for all four to be non-functioning at the same time. Flavor comes from our sense of smell.
The most common cause of a change in our sense of smell is due to infection. Both the common cold and sinusitis can cause loss of our sense of smell known as anosmia. This is usually temporary and recovery occurs once the infection has cleared. Much less frequently the loss of the sense of smell may become permanent.
The second most common cause of loss of the sense of smell is head trauma. Sudden shifting of the brain within the cranial cavity can actually shear off the fine olfactory nerves that enter the nasal cavity from the cranial cavity. These nerves usually do not heal and the loss of sense of smell is permanent.
In all cases of smell and taste disorders, imaging of the sinuses and sometime the brain is needed to determine if there is a cause that can be treated.