The causes of many chronic daily headaches aren't well-understood. True (primary) chronic daily headaches don't have an identifiable underlying cause.
Conditions that might cause nonprimary chronic daily headaches include:
Inflammation or other problems with the blood vessels in and around the brain, including stroke
Infections, such as meningitis
Intracranial pressure that's either too high or too low
Brain tumor
Traumatic brain injury
Medication overuse headache
This type of headache usually develops in people who have an episodic headache disorder, usually migraine or tension type, and take too much pain medication. If you're taking pain medications - even over-the-counter - more than two days a week (or nine days a month), you're at risk of developing rebound headaches.
Risk factors
Factors associated with developing frequent headaches include:
Female sex
Anxiety
Depression
Sleep disturbances
ObesitySnoring
Overuse of caffeine
Overuse of headache medication
Other chronic pain conditions