Most effective: Large, flat areas like the arms and legs. Least effective: Curved areas the same as the underarms, and may even cause significant trauma on the face and also other thin skinned areas. Are you still in college? If you are, look at your school district's website. http://www.cruzenews.com/wp-content/plugins/zingiri-forum/mybb/member.php?action=profile&uid=1984279