Can a tension headache have no cause? i live about as a stress free life as one could have and have a constant tension headache from dawn to dusk.

Don't need stress to: Have "tension" headache - even though they are often associated with stress. Do you know how to do progressive muscle relaxation? Some people easily carry tension in the neck & upper back. This builds over time. Have you considered acupuncture, yoga, stretching or massage to decrease some of that muscular tension?

Headache: Evaluation for the type of headache is recommended, especially by a neurologist. Also, other causes need to be ruled out, such as blood pressure changes or effect of medications.