Why do we get bad breath?!

Why do we get bad breath?

i understand that people either don't brush correctly, and don't take care of their mouth or have that infection starting with a t, ive forgotten it now; but why do some people get that infection, and others don't? i mean; im not one to go around and smell peoples' breaths, [lol] but i usually notice it; and the people whom don't have have bad breath always share the same smell on their breath. But, i was wondering what is the treatment that dentists will usually perscribe if you do have that infection?
Thanks.

I believe everyone has the same types of bacteria in their mouth, but some bacteria dominate over others. Some people have more cavity enhancing bacteria which means they will be more susceptible to tooth decay. Others will not have tooth decay problems, but will develop gum disease. And then some poor souls will get both...
Bad breath can be just from poor hygiene, which leaves the biodegrading food, similar to your trash can, to start producing an odor. If this habit continues over a long period of time...years, then the body has to try to fight back. The disease process is actually a defense mechanism against the bacteria. Bacteria cause acids, acids produce toxins and break-down, immune system kicks in and their battle produces the results of decaying tissue and infection.....this stinks. The treatment for gum disease can be a simple as a routine cleaning either every 3, 4 or 6 months. Or scaling under the gum tissues while the teeth are numb followed by 3-4 month maintenance cleanings.
The sinus can cause problems with bad breath too. If your sinuses are infected, that tissue is also decaying and the smell is very bad. Acid reflux can also cause a foul smell in the breath. Rotten food back-wash....that must smell bad...lol