The most common causes are odor producing biofilm on the back of the tongue, below the gumline, and in the pockets created by gum disease between teeth and the gums. This biofilm results in the production of high levels of foul odors. The odors are produced mainly due to the breakdown of proteins into individual amino acids, followed by the further breakdown of certain amino acids to produce detectable foul gases. Volatile sulfur compounds are associated with oral malodor levels, and usually decrease following successful treatment. Other parts of the mouth may also contribute to the overall odor, but are not as common as the back of the tongue. These locations are, in order of descending prevalence, inter-dental and sub-gingival niches, faulty dental work, food-impaction areas in between the teeth, abscesses, and unclean dentures. Oral based lesions caused by viral infections like herpes simplex and HPV may also contribute to bad breath.