Epidemiology describes how often a condition occurs and in whom. For headache, the figures for each pattern also set the starting expectations for a diagnosis.
Headache disorders affect about 40% of people, an estimated 3.1 billion worldwide in 2021. They rank among the top three neurological conditions from age 5 to 80. They are more common in females.
Tension-type headache
Tension-type headache is the most common primary headache. Episodic tension-type headache, meaning fewer than 15 headache days per month, is reported by more than 70% of some surveyed populations. Chronic tension-type headache is unremitting and more disabling. The same 15-day line separates episodic from chronic forms.
Migraine
Migraine affected about 1.16 billion people in 2021, up from about 733 million in 1990. Absolute rates are higher in females, but the rise was fastest in males and in adolescents under 20. Migraine typically begins at puberty and peaks at ages 35–45. A typical attack lasts 4–72 hours with nausea or sensitivity to light and sound, sometimes preceded by reversible aura (temporary neurological symptoms, most often visual).
Chronic migraine means headache on at least 15 days per month for more than 3 months, with migraine features on at least 8 of those days. Characterizing frequent headache requires a diary kept over at least 1 month.
Cluster headache
Cluster headache is rare, affecting up to 1 in 1000 people. It is male-predominant. Modern clinic series give a ratio around 2.5 men to each woman, while older population figures reach 6 to 1. The ratio falls with age and over time. Untreated attacks last 15 minutes to 3 hours, averaging 45–90 minutes. Mean onset is in the third decade of life.
From frequency to pre-test probability
Pre-test probability is how likely a diagnosis is before further testing, and these patterns set it before pattern recognition begins. Bilateral pressure in a busy adult is most often tension-type headache. Recurrent disabling attacks with nausea favor migraine. A pacing patient with a red tearing eye points strongly toward cluster headache. The patterns themselves are described in Headache Clinical Presentation. How frequency and pattern shape the outlook, including chronification, is covered in Headache Prognosis and Complications.