Epidemiology of Itch.

Epidemiology is the study of disease frequency and the associations between risk factors and outcome in a population. Clinical populations are highly selective and depend for instance on perceived severity of symptoms and access to health services. Assessment of a disease in the community and in specific populations is an important measure for the purpose of health planning as well as for the understanding of associations between disease and factors in the environment. Itch is definitely the most frequent symptom of the skin and can occur in acute and chronic skin diseases and other diseases like end-stage renal disease, cholestasis, and hematological, neurological, and psychiatric diseases. This diversity may explain why research on the epidemiology of itch was disregarded for a long time. A recent European study demonstrated that the prevalence of itch among dermatological patients is 54.4%. The prevalence of acute itch in the general population is 8.4% and for chronic itch it is 13.5%; however, with a recurrent symptom it is important to consider different prevalence estimates (point, 12-month, and lifetime prevalence). The lifetime prevalence of chronic itch in the general populations is 22%, demonstrating that more than 1 in 5 people experience chronic itch once in their life. This shows that research in this field should not only focus on patients. This chapter briefly summarizes major facts on the epidemiology of itch in the general population and in some patient populations.