Epidemiology of smell and taste dysfunction.

How common are smell and taste disorders? How many persons suffer total loss or partial loss? What factors determine such dysfunction? Answers to these questions are not straightforward. Estimates of prevalence are influenced by a multitude of interacting factors, including age, gender, occupation, geography, air and water quality, climate, ethnicity, genetics, education, and health, to name a few. In reality, population estimates of chemosensory disorders vary widely among studies, reflecting not only differential sampling of such variables, but the types of sensory tests that have been employed and the choice of cutoff points to define abnormality. While population-based studies likely provide the most accurate assessments of overall prevalence, even their findings vary dramatically. Nonetheless, there is unanimity among studies that chemosensory disorders are very common in countries where epidemiologic data have been collected, with higher prevalence in men than in women and in older than in younger persons. Moreover, population-based studies have identified, or confirmed observations of case-control and other studies, a wide range of factors that impact the chemical senses. This review describes the major epidemiologic studies that have estimated the prevalence of chemosensory disorders and explores factors involved in producing such disorders within the aging population.