Anosmia is the loss of the sense of smell. Anosmia may have many different causes. Viral infection, head trauma, surgery, allergies, chronic sinusitis, sinonasal polyps, benign, or malignant tumors may cause anosmia. Some patients have no identified cause. If no obvious cause is seen on exam, a CT or MRI may be ordered to better observe the anatomy around the olfactory (smell) nerves. Treatment is directed toward the underlying cause, if one is found, and may include medical treatment for infections, allergies, or inflammatory conditions, or surgery to relieve nasal obstruction.