The vast majority of headaches are benign and self-limiting. Common causes are tension, migraine, eye strain, dehydration, low blood sugar, and sinusitis. Much rarer are headaches due to life-threatening conditions such as meningitis, encephalitis, cerebral aneurysms, extremely high blood pressure, and brain tumors. When the headache occurs in conjunction with a head injury the cause is usually quite evident. A large percentage of headaches among females are caused by ever-fluctuating estrogen during menstrual years. This can occur prior to, during or even midcycle menstruation.

Treatment of uncomplicated headache is usually symptomatic with over-the-counter painkillers such as aspirin, paracetamol (acetaminophen), or ibuprofen, although some specific forms of headaches (e.g., migraines) may demand other, more suitable treatment. It may be possible to relate the occurrence of a headache to other particular triggers (such as stress or particular foods), which can then be avoided.

While, statistically, headaches are most likely to be harmless and self-limiting, some specific headache syndromes may demand specific treatment or may be warning signals of more serious disorders. Some headache subtypes are characterized by a specific pattern of symptoms, and no further testing may be necessary, while others may prompt further diagnostic tests.

Headache associated with specific symptoms may warrant urgent medical attention, particularly sudden, severe headache or sudden headache associated with a stiff neck; headaches associated with fever, convulsions or accompanied by confusion or loss of consciousness; headaches following a blow to the head, or associated with pain in the eye or ear; persistent headache in a person with no previous history of headaches; and recurring headache in children.

The most important step in diagnosing a headache is for the physician to take a careful history and to examine the patient. In the majority of cases the diagnosis will be tension headache or migraine, both of which can be managed on the basis of a clear-cut clinical picture. Where doubt remains, or if there are abnormalities detected on examination, further investigations are justified. Computed tomography (CT/CAT) scans of the brain or sinuses are commonly performed, or magnetic resonance imaging (MRI) in specific settings. Blood tests may help narrow down the differential diagnosis, but are rarely confirmatory of specific headache forms.