Anosmia (loss of sense of smell) is caused by head injury and tumours of the olfactory groove (e.g. meningioma, frontal glioma). It is often lost, occasionally permanently, after upper respiratory viral infections and diminished when the nose is blocked.
Anosmia is the partial loss of smelling senses which is due to presence of any obstruction in nasal passages. Sometimes, the cause may be polyps.