According to the latest research, 9% of men and 12% of women in the U.S. experience at least 1-2 headache episodes per month. And, more than 4% of the U.S. population suffers from frequent headaches, defined as headaches that occur at least 180 days a year. Needless to say, headaches have become a social and economic burden in the United States, as well as other parts of the world. Scientists have identified over 300 causes for headaches. Various pain-sensitive structures and tissues including the skin, subcutaneous tissue, muscles, arteries, periosteal bone covering, and the upper cervical and facial nerves produce headaches when irritated or injured. Fortunately, only a handful of causes are responsible for the majority of headaches.