Global epidemiology of itch from 1990 to 2017: gender, age, sanitation, and air pollution as risk factors

Background: Itch is a symptom with significant physical, psychological, and financial burden worldwide. Symptom-specific and demographic risk factors have been published although community-level risk factors have not been thoroughly studied. Objectives: To describe the epidemiological risk factors of itch and to present a hypothesis that can account for these trends. Materials and methods: Itch incidence, prevalence, and years lost to disability (YLD) by age, sex, world region, socio-demographic index, percent of population using basic sanitation services, mortality due to air pollution, and gross domestic product (GDP) per capita were obtained from the University of Washington Institute for Health Metrics and Evaluation Global Burden of Disease (GBD), World Health Organization Global Health Observatory (WHO GHO), and Worldometer databases. Linear regression models were utilized to analyze the relationship of sanitation, air pollution, and GDP with itch incidence, prevalence and YLD. Results: Female sex and age were positively associated with higher incidence of itch. The percent of population using basic sanitation services was also positively correlated with itch incidence, prevalence, and YLD (P<0.001). Mortality rate due to air pollution was negatively associated with itch incidence, prevalence, and YLD (P<0.001). However, GDP per capita was not associated with the incidence (P=0.5), prevalence (P=0.8), and YLD (P=0.7) of itch. Conclusions: The “hygiene hypothesis” might explain global trends of itch as more industrialized countries have higher itch incidence rates. Thus, approaches which target molecular pathways involved in the “hygiene hypothesis” may lead to a decreased global itch burden.