1. MedlinePlus: Headache
(Mayo Foundation for Medical Education and Research) External Compression Headaches. (American Headache Society, Committee on Headache Education) Headaches: Get medical help right away if you have a headache after a blow to your head, or if you...
http://www.nlm.nih.gov/medlineplus/headache.html

2. Headache causes and treatment information from iVillage Total Health
External compression headache. Primary headaches are often a tension headache, migraine or cluster headache. According to the American Council for Headache Education, more than 90 percent of headaches are primary headaches.
http://yourtotalhealth.ivillage.com/headaches.html?pageNum=3

3. External compression headaches - MayoClinic.com -- Mayo Clinic Medical Information And Tools...
External compression headaches are caused by any type of head wear that places pressure on the head including tight hats, helmets, headbands and goggles. Any head wear that puts continuous pressure on your forehead or scalp can lead to what's...
http://www.mayoclinic.com/health/external-compression-headaches/DS00642