A tension headache is usually caused by tightening in the muscles of the face, neck, scalp, or shoulders as a result of stress or poor posture. These tight muscles pinch nerves or their blood supply, creating the sensation of pain and pressure. Relaxation of the muscles usually brings about immediate relief. Often a tension headache can be worsened (or improved) by applying hand pressure to trigger points on the neck muscles. A trigger point is the central area of tension in the muscle.