Headaches are one of the most common forms of pain. More than 45 million Americans have headaches severe enough to require the help of a health care professional. Headaches occur when pain-sensitive nerve endings around the scalp, in the blood vessels that surround the skull, in the lining around the brain, and in other areas around the head send impulses to the part of the brain that interprets pain signals from the rest of the body. Some headaches are related to tender spots in head, neck, and shoulder muscles.
NCCAM Clinical Digest: Headaches and Complementary Health Practices