The more dry your mouth, the more chance you will have bad breath. It has to do with the amount of oxygen available in your saliva. The bacteria that cause bad breath, thrive in an anaerobic (no oxygen) environment. When your mouth gets dry, your saliva disappears or gets thicker, representing the reduction of Oxygen. The bacteria sense this difference and when the Oxygen level drops, they start to produce Odorous Sulfur Compounds, such as Hydrogen Sulfide (the rotten egg smell). By the way, from the age of 25 on, we all start to produce less saliva. It goes downhill from that point on, so there is always a greater chance to produce bad breath as we all get older.