Headache is a term used to describe pain or discomfort in the head. The condition may be triggered by a number of factors.

Many areas of the head can become painful. These include the nerves extending over the scalp and specific nerves located in the face, mouth and throat. Other areas of the head, such as jaw muscles and the blood vessels located on the surface and base of the brain, are also susceptible to pain. The bones of the skull and brain tissue cannot become painful because they do not contain pain-sensitive nerve fibers.  

Pain occurs when the ends of pain-sensitive nerves are stimulated. Known as nociceptors, the nerve endings may be stimulated by a number of factors including stress, dilation of blood vessels and muscle tension. When a nociceptor is stimulated, it transmits messages to the nerve cells in the brain. This alerts the brain that part of the body is in pain.

Different areas of the body send different pain messages to the brain. The message is based on the location of the affected nociceptor. For example, a person who experiences pain in the finger is responding to nociceptors located in the hand.    

Headache is one of the most common medical complaints. According to the American Council for Headache Education, nearly 90 percent of men and 95 percent of women have had at least one headache during the past year. Although the condition can cause debilitating pain, headaches are rarely due to life-threatening disorders.