Most effective: Large, flat areas like the arms and legs. Least effective: Curved areas the same as the underarms, and that can cause significant trauma for the face and other thin skinned areas. Most ionic flat irons are made to produce negative ions which essential for styling your hair. https://images.google.bi/url?q=http://www.suubinc.com/7-essential-tools-every-aspiring-hairdresser-should-own/