Headaches are caused by a chemical reaction in your brain combined with the muscles and nerves of your neck and head.
When experiencing a severe, throbbing headache, a person often places his hands on both sides of his head and claims, "It feels like my brain is pushing to get out, so it feels better to hold it in." This sensation gives a false impression that the brain itself is enlarging and causing the pain sensation. Interestingly, brain tissue does not feel pain in the same way skin or other organs do. Because the brain is encased in a hard, protective covering, it has not developed to respond to touch or pressure sensations like other, more exposed parts of our bodies have. Indeed, a brain surgeon can cut brain tissue in an awake patient without the patient feeling the knife.
Head pain instead occurs because of activation or irritation of structures that do sense pain: skin, bone or neck joints, sinuses, blood vessels, or muscles. When a person has a brain tumor, pain is usually a late symptom to develop--brain tumors generally only cause pain when they have grown large enough to damage bone or stretch blood vessels or nerves. Neck problems may also result in head pain, with pain from the neck and back of the head often radiating over the top of the head to an eye. Sinus infection or inflammation (usually occurring as part of an allergy reaction), however, is an uncommon cause of recurring headaches. Interestingly, Roger Cady and Curtis Schneider of the Headache Care Center in Springfield, Mo., have shown that 25 to 30 percent of migraine sufferers report nasal symptoms during their typical migraine episodes, and nearly 98 percent of people who believed they had sinus headaches were experiencing a migraine.