November 2009

Frequency (Incidence) of Smell Loss (Hyposmia) in the U.S.

There appears to be much confusion and misunderstanding about the frequency by which hyposmia occurs in the U.S. Most physicians consider this loss rare. However, evaluation of its incidence using easily obtainable data suggests that as many as 21 million people in the U.S. suffer from chronic loss of smell. These are some of the data that relate to these incidence numbers.

1. A survey of smell was performed by the Fragrance Foundation in 1981. Five thousand questionnaires were distributed throughout the U.S. and 2000 were returned and analyzed. Seven percent of patients reported that they had a chronic loss of smell. If this is extrapolated for the U.S. population than 21 million people in the U.S. have a chronic loss of smell.

2. Adverse effects of therapeutic drugs. The Physician Desk Reference (PDR) is a compilation of all current drugs approved by the FDA for use in the U.S. The number of patients taking these drugs in various categories on a yearly basis is quite large. Fifty million patients take antihypertensives, 20 million take hypoglycemic agents (they have diabetes), 10 million take antidepressants, 10 million received chemotherapeutic agents for cancer, and 30 million take antibiotics. Included in this listing are all the adverse effects of these drugs in addition to their positive therapeutic effects. Listed among these adverse effects are loss and/or distortion of taste and/or smell which range from 1-5% among many of these drugs. On the basis of these data as many as 27.5 million patients may exhibit transient or permanent loss and/or distortion of taste and/or smell on the basis of adverse drug reaction.

3. Clinical Effects

   1. PIHH. The most common case of smell loss in the U.S. is following an influenza-like illness. About 30 million people in the U.S. develop a flu-like illness yearly and about 1% of them develop a permanent loss of smell or about 300,000 people yearly.

   2. Head Injury. About 1.6 million patients in the U.S. experience a significant head injury yearly. About 60% of these patients experience a significant impairment in their taste and/or smell function or about 900,000 patients yearly.

   3. Allergic Rhinitis. About 25 million patients in the U.S. experience significant perennial or seasonal allergies. About 5% of these patients experience transient or permanent loss of smell and/or taste because of these symptoms or about 1.25 million patients.

4. Neurodegenerative Disorders. Patients with multiple sclerosis (MS), Parkinson’s disease and Alzheimer’s disease experience loss of smell associated with the other neurological symptoms of their disease process. While the number of patients with each of these disorders is not firmly established the number of patients with MS includes 250,000 patients, Parkinson’s disease 300,000 patients and Alzheimer’s disease 4 million patients. Estimates suggest that about 37,000 patients with MS exhibit hyposmia, 270,000 with Parkinson’s disease and 400,000 with Alzheimer’s disease.

5. Clinic Visits to U.S. Physicians. There were 880 million visits by patients to physicians in 2006. If only 1 in 1000 patients or 0.01% complained of smell loss then 880,000 patients had either a transient or chronic loss of smell.

These estimates of frequency of hyposmia in the U.S. are only a portion of patients who may complain of smell loss. Patients in nursing homes, in chronic care facilities and patients with cancer with or without treatment with chemotherapy or x-irradiation also exhibit hyposmia, associated loss of food flavor and subsequent loss of appetite and anorexia.

Far from being a rare occurrence hyposmia is a common clinical event in the U.S. which has gone unrecognized by most physicians.