Significant Decline in the Incidence of Behçet's Disease in South Korea: A Nationwide Population-Based Study (2004-2017).

BD incidence decreased from 2004 to 2017 in the Republic of Korea. This decline in incidence might be attributable to changes in environmental factors, including a reduction in the burden of infectious diseases in the past decades and improvement in oral health during childhood. The unprecedented decline in the incidence of BD in the Republic of Korea without major changes in genetic background suggests that environmental factors are very important to the development of BD.