The nebulising diffuser works by forcing an air current through a narrow micro-tube which increases its velocity. The pressure at the exit point of the narrow micro-tube is subsequently reduced.
Due to the fact that there is no heat involved, the original chemical structure of the essential oils are not altered or destroyed. Therefore, the essential oil molecules are able to be quickly inhaled and absorbed by the human body in their most natural, original state.
Thanks Winnie for putting this explanation together!
Reference – http://organicaromas.com/pages/how-it-works