The epidemiology of chronic daily headache.

Chronic daily headache (CDH) is a fairly common but disabling disorder that disproportionately affects women and afflicts individuals across all stages of adulthood. It is a dynamic disorder, marked by relatively high rates of remission and incidence. To some extent, this may be due to the accepted, but not empirically supported, cut-point of 15 headache days per month. The purpose of this article is to understand the CDH classification; determine the prevalence and associated demographic profile of CDH as derived from population-based studies; outline identified risk factors for development or persistence of CDH; and understand which risk factors may be more amenable to intervention. Understanding the factors that put people at risk for developing CDH helps to inform possible clinical interventions and also determines which individuals may be most in need of preventive efforts.