Final answer:
The primary cause of halitosis is increased anaerobic bacterial activity at the back of the tongue, not increased salivation, loss of teeth, or a lack of amylase in saliva.
Step-by-step explanation:
Halitosis, commonly known as bad breath, is primarily caused by increased anaerobic bacterial activity at the back of the tongue. When plaque accumulates on the teeth, anaerobic bacteria colonize the gingival space, including Porphyromonas, Streptococcus, and Actinomyces, contributing to bad breath. Increased saliva can actually help to wash away food particles and bacteria, reducing halitosis, not causing it. Likewise, a lack of amylase in saliva would not cause halitosis directly, but rather affect the breakdown of starches in the mouth.
The loss of teeth does not cause halitosis directly, but missing teeth can contribute to difficulty in cleaning the mouth adequately, potentially providing a space for bacteria to thrive.