A secondary headache is a symptom of a disease that can activate the pain-sensitive nerves of the head. Any number of conditions — varying greatly in severity — may cause secondary headaches.
Arterial tears (carotid or vertebral dissections)
Blood clot (venous thrombosis) within the brain — separate from stroke
Brain aneurysm (a bulge in an artery in your brain)
Brain AVM (arteriovenous malformation) (an abnormal formation of brain blood vessels)
Brain tumor
Carbon monoxide poisoning
Chiari malformation (structural problem at the base of your skull)
Concussion
Encephalitis (brain inflammation)
Giant cell arteritis (inflammation of the lining of the arteries)
Glaucoma
Hangovers
Influenza (flu)
Intracranial hematoma (blood vessel ruptures in the brain)
Medications to treat other disorders
Meningitis (inflammation of the membranes and fluid surrounding your brain and spinal cord)
Monosodium glutamate (MSG)
Overuse of pain medication
Post-concussion syndrome
Pressure from tight-fitting headgear, such as a helmet or goggles
Pseudotumor cerebri (increased pressure inside the skull)
Sinus inflammation and congestion
Stroke
Trigeminal neuralgia (disruption of the nerve connecting the face and brain)
External compression headaches (a result of pressure-causing headgear)
Ice cream headaches (commonly called brain freeze)
Rebound headaches (caused by overuse of pain medication)
Sinus headaches (caused by inflammation and congestion in sinus cavities)
Spinal headaches (caused by low levels of cerebrospinal fluid, possibly the result of trauma, spinal tap or spinal anesthesia)
Thunderclap headaches (caused by low levels of cerebrospinal fluid, possibly the result of trauma, spinal tap or spinal anesthesia)