Poor dental habits and eating certain foods contribute to halitosis, or bad breath, according to WebMD. Smoking cigarettes and chewing tobacco also contribute to bad breath.
Foods that are particularly odorous, such as garlic and onions, are common causes of bad breath. Failure to brush and floss daily allows bacteria to build up between the teeth, which creates odor in the mouth. Failure to properly clean dentures has the same effect, says WebMD.
Bad breath also sometimes indicates the presence of gum disease or dental cavities, WebMD states. Dry mouth leads to halitosis as well. Additionally, respiratory tract infections, chronic acid reflux and diabetes are possible causes.