What Causes Loss of Smell (Anosmia)?

More than 200 medical conditions have been associated with olfactory changes and loss. Abnormalities in smell and taste functions often accompany and even signal the existence of several diseases or unhealthy conditions, including obesity, diabetes, hypertension, malnutrition, and some degenerative diseases of the nervous system. ¹

However, loss of sense of smell is usually the result of nasal congestion or blockage and isn’t serious. Temporary loss of smell is common with colds, sinus infections (sinusitis) and nasal allergies, such as hay fever (allergic rhinitis). Smell is often lost with disorders that prevent air from reaching the part of the nose where smell receptors are located (the cribriform plate, located high in the nose). These disorders include nasal polyps, nasal septal deformities and nasal tumors. Some loss of smell occurs normally with aging. In most cases, there is no obvious or immediate cause, and there is no treatment.
Some of the known causes of anosmia include:

• Aging
• Degenerative brain diseases such as Parkinson’s and Alzheimer’s ^{2 3}
• Disorders of the endocrine system
• Drugs (including amphetamines, estrogen, naphozoline, phenothiazines, reserpine and prolonged use of nasal decongestants)
• Enlarged adenoids
• Head trauma (estimated 20% of cases) ⁴
• Nasal polyps
• Nasal or sinus illnesses (estimated 15% of cases)
• Nasal or sinus surgery
• Radiation therapy
• Smoking or exposure to tobacco smoke
• Tracheostomy
• Tumors of the nose or brain
• Upper respiratory infections (including the common cold) (estimated 25% of cases) ⁵

For prolonged loss of smell, patients should consult their doctors. It is difficult to measure loss of smell, and it rarely occurs in just one nostril. So a physician usually begins by testing each nostril separately with a common, non-irritating odor such as perfume, lemon, vanilla or coffee. Polyps and rhinitis are obvious causal agents for which a physician will look. Imaging studies (X-ray, CT, MRI) of the head may be necessary to detect brain injury, tumors or other causes. In some cases, surgery (biopsy) to remove a piece of the cell tissue responsible for smell (olfactory epithelium) may be needed to make a diagnosis. In about 22% of cases, the cause is never determined and the loss of smell is classified as idiopathic – cause unknown