University of Iowa Health Science Relations and
Phillip Lainson, DDS, MS
Professor Emertus and Former Head of the Periodontics
First Published: 2000
Last Revised: December 2004
Peer Review Status: Internally Peer Reviewed

If you step onto an elevator and the other people gasp and squeeze into a corner, you may have bad breath, the television commercials say.

But bad breath isn't always the result of choosing the wrong mouthwash or toothpaste, a University of Iowa dentist says.

The cause of bad breath might be the food you ate for lunch, out-of-control diabetes, or perhaps postnasal drip.

"The first step in dealing with bad breath is to figure out what is causing it," says Dr. Phillip Lainson, professor emertus and former head of the periodontics department at the UI College of Dentistry. "You may brush your teeth four times a day and use mouthwash regularly; but if you have diabetes, that will not help at all," he says.

Smoking, tonsillitis, diseases of the lungs and air passages, kidney dysfunctions, and leukemia also are among possible medical causes of undesirable mouth odors.

Bad breath also may be a sign of oral diseases such as "trench mouth"--an inflamation of the mouth and gums--or advanced periodontal disease involving the gums and foundations of the teeth.

If you breathe mainly through your mouth, you may have bad breath because of dryness. Saliva helps wash your mouth and dissolve food particles. Lack of saliva can allow these particles to sit in your mouth longer, so they decompose and cause odor, Dr. Lainson says.

You may experience bad breath in the morning because food particles have had several hours to decompose. Brushing your teeth before going to bed can help reduce morning mouth odor.

The foods you eat also may affect your breath. Onions and garlic can cause bad breath that lasts for hours. But these odors do not originate in your mouth. Instead, odors are absorbed from foods that are in your digestive system, he says. These odors are then carried by the blood to your lungs where they are exhaled.

"A lot of bad breath is caused by poor oral hygiene," Lainson says.

The oral cavity has millions of bacteria. Some float loose. Others live in areas that are less accessible to cleaning, such as between teeth, beneath gum edges, and on the tongue.

When the teeth and mouth aren't cleaned properly, these bacteria can collect around teeth or dentures and work to decompose the food. "This decomposition may be an important source of mouth odor," Lainson says.

"Good oral hygiene involves good gum and tooth root care, in addition to brushing your teeth," Lainson says. "You may be brushing three times a day but not getting access to all parts of your teeth. You may not be cleaning around the gum edge.

Your dentist can demonstrate the proper techniques of gum and tooth root care.

Mouthwashes can offer very brief relief from bad breath. "But you must realize that you may be masking the odor rather than eliminating the cause," Lainson says. "A lot of mouthwashes claim to be antibacterial but there is no evidence that they are killing the bacteria that produce odors. And not all mouth bacteria are harmful to the teeth or breath."

If a person practices good oral hygiene and still has bad breath, the cause may lie elsewhere, Lainson says. "Having people avoid you in an elevator may be the least of your problems. You could have a serious dental or medical problem. So, if you have bad breath, do check it out with your dentist or doctor."