Loss of smell is called anosmia. Anosmia can have numerous causes, and your primary care doctor
can help you figure out what is going on.
By far the most common causes of anosmia are inflammation and mucus coating the inner lining of the nasal passages. Chronically, this would be most likely due to allergic rhinitis, or nasal allergies. Therefore, if you have any symptoms like chronic nasal congestion, runny nose, sneezing, and cough you should mention these to your doctor. Allergic rhinitis is relatively easy to treat with simple medications. Alternatively, a mechanical obstruction in the nose, such as from a nasal polyp or a deviated nasal septum could have a similar effect.
There are also numerous other less common causes of loss of smell. For example many chronic medical problems, such as diabetes, can be associated with anosmia. You will need to talk with your primary care doctor to see if any of your other medical problems might be associated with this problem.
Alternatively, sometimes age alone can be associated with a gradual decrease in your ability to smell acutely and this can be normal.
Start by talking with your primary care doctor, who will help you determine if there is something that needs to be treated.