Good question...I should have been more specific. Ionic hair dryers aren't the issue. Some products (ISO, Joico, and several other Zotos brands are forthright about using this technology) ionically charge their ingredients to have a positive charge so that negative-charged hair attracts their products, in theory, creating more evenly healthy-acting hair. However, when all the hairs next to each other have the same charge, like repels like and spider weby frizz is created.
Ionic hair dryers, from what I've read, don't leave ion charges on the hair.