Bad breath is usually caused by certain foods or ingested substances as garlic, alcohol, and because of cavities or other dental illnesses. Also because of food fermentation in the mouth. This last one is favored at night, since the production of saliva dramatically decreases while we sleep. Certain germs take advantage of this circumstance to augment the dental plaque that forms the tartar when solidifying.
Also, other microorganisms anaerobically decompose the nutritious remains caught between the teeth. The early morning bad breath can be increased by gases been reabsorbed at the level of the colon and are liberated through the lungs’ surface when breathing.