Who invented mouthwash? is debatable. Some would suggest the Joseph Lister (Listerine) invented it. Yet other accounts date mouthwash back to Biblical times. Since mouthwash is used for the purpose of washing the mouth, It is probable that someone long ago used water or another substance to rinse and freshen the mouth. So it is really anybody’s guess as to who invented mouthwash. But aren’t you glad they did?