What causes a headache?

Headaches are classified as primary or secondary.

• A primary headache means the headache itself is the main medical problem, although other factors, such as muscle tension or exposure to certain foods, may be identified. Other contributing factors include medicines, dehydration, or hormone changes.

• A secondary headache is related to an underlying medical condition. An example of this would be a headache due to neck injury, eye problems, jaw, teeth or sinus infection.