Probably close to 90% of tension headaches are caused by trigger points. People who have headaches (including migraines) are almost twice as likely to have postural abnormalities, including head-forward posture, and also have trigger points in the back of the neck, particularly in the suboccipital muscles. People who suffer from both migraines and tension-type headaches are far more likely to have a greater number of active trigger points. The greater the number of active trigger points, the more frequent and severe the headaches. With one-sided headaches, a greater number of active trigger points are found on the same side as the headache. Trigger points that cause headaches are most likely located in the trapezius, posterior neck, sternocleidomastoid, temporalis, facial, and occipitalis muscles, and usually multiple muscles are involved.