Respiratory infections, sinusitis, and head trauma are the most common causes of anosmia.
Anosmia arises when any obstruction inside the nasal cavity blocks odors from reaching the olfactory area. Besides, damage to the olfactory epithelium, nerves that carry the signals from the epithelium to the brain or the part of the brain that perceives smell can also result in anosmia. Medical conditions like allergic rhinitis, nasal polyps (growths), atrophic rhinitis and chronic sinusitis are common diagnoses. The major causes include:
- Head trauma. Most common in young adults.
- Viral infections and Alzheimer’s disease in older adults
- About 14 to 26% of all presenting cases of hyposmia or anosmia are due to upper respiratory tract infections (URI) (URI refers to the infection of nose, sinuses, pharynx or larynx), esp. influenza infection.
- Prior head and neck radiation, recent nasal or sinus surgery, nasal and brain tumors, and toxins are also implicated as causes of anosmia.
- Exposure to the following drugs may cause anosmia in susceptible persons:
Amphetamines, enalapril, estrogen, naphazoline, phenothiazines, reserpine
- Prolonged use of decongestants is also a cause. Patients may also give history of exposure to toxins like cadmium, or manganese.
- Cecil Medicine, 23rd Ed.
- The Merck Manual of Patient Symptoms.