Does drinking prune juice cause bad breath?

May or may not: Bad breath (halitosis) is usually a multifactorial occurrence. The most plausible cause is the luffy epithelial layer of the tongue, which can collect and hide millions of bacterias and chemicals, hence the bad taste or odor. Many foods and drinks can exacerbate such process. Other factors are accumulation of plaque & tartar build up between the teeth & restorations, cavities, & sinus drainage.

No: Bacteria in your mouth cause bad breath. See your dentist or periodontist to have an evaluation and have your teeth cleaned.