What are the causes of bad breath? In more than 90 percent of cases, ongoing bad breath is caused by the activities of bacteria that are naturally present in the mouth. There are many different species of bacteria living in our mouths and they normally do us no harm; in fact, they are an integral part of a healthy mouth, helping to digest food and keeping more dangerous bacteria from making themselves at home. Bacteria live on the cells that line the mouth, in the plaque that builds up on the teeth, and in the saliva. They collectively create a biofilm in the mouth - a layer of material containing many different organisms, thriving together as a community.

Bacterial activities that can be a bad breath cause include the breaking down of dead epithelial cells (cells that line the inside of the mouth that are sloughed off and replaced frequently), blood cells, food particles, and proteins and other molecules found in saliva. Bacteria are the janitors of our mouths, but unfortunately, some of them create bad-smelling compounds that are causes of bad breath, while they do their work.

Certain species of bacteria are particular culprits in what causes bad breath. These are the anaerobes - bacteria that live in the absence of oxygen. When they break down substances in the mouth, they produce a byproduct, a bad breath cause known as volatile sulfur compounds. (Think of the rotten smell of sulfur, or even worse, hydrogen sulfide, which is the smell produced by a rotten egg.) There are several different volatile sulfur compounds produced by these bacteria and they are all causes of bad breath. They are detectable, and offensive, even when they are only present in relatively small amounts.

The anaerobic bacterial causes of bad breath thrive everywhere in the mouth where they are exposed to minimal amounts of oxygen: between the teeth (often in particles of food that have lodged there), between the papillae of the tongue (the little bumps that house the taste buds), in crevices and folds of the cheeks and gums, and in pockets formed between the teeth and gums in gum disease. The matrix (non-living substance) of the biofilm itself can shield them from oxygen. Often, what causes bad breath is some unhealthy situation in the mouth such as gum disease, that allows the anaerobic bacteria to multiply to unusual numbers.

So when you ask, "What are the causes of bad breath," you will get various answers: bacteria are part of what causes bad breath, but some other condition in the mouth is likely to be a contributing bad breath cause as well.