Chronic daily headache (CDH) is a common neurological condition that affects 1-4 % of the general population. Most individuals with CDH originally suffered from episodic headaches, but over time, this developed into CDH. Although the pathophysiology of CDH is not fully understood, recent clinical and epidemiological studies suggest some risk factors that are associated with an increased risk of transformation from episodic headaches. If risk factors can be identified, they could provide a base for aggressive preventive intervention and thus decrease the transformation from episodic headaches to eventual CDH. In this article, we review and summarize the current data on risk factors for CDH.