Halitosis is the medical term for bad breath. It can occur when decaying matter (e.g., food particles, dead cells) accumulates in the mouth and combines with bacteria to produce an unpleasant odor. Bacteria thrive in warm and moist areas such as the mouth, especially on the rough surface of the tongue. When large amounts of decaying matter exist, the bacteria normally present in the mouth consume it and expel foul-smelling by-products.

In addition, nasal discharge or mucus can accumulate at the back of the throat, fostering the growth of bacteria and producing an unpleasant odor noticeable in a person’s breath.

Certain foods (e.g., garlic, onions) and beverages (e.g., coffee, alcohol) can produce a distinctive breath odor. After digestion, molecular components of these products are carried by the bloodstream to the lungs, where their odor is released with breath as a person exhales. This continues until the food or drink has been completely eliminated from the body or it can be reduced by brushing the teeth.

Halitosis is fairly common and most people experience it at some point. For example, bad breath that occurs upon waking in the morning (morning breath) is caused by a decrease of saliva in the mouth during sleep. Saliva helps to keep the mouth moist and rid it of decaying food particles, bacteria and dead cells that can accumulate there.

In most cases, halitosis is temporary – it is resolved when saliva production is restored, when certain foods or beverages exit the body, or when halitosis caused by poor dental hygiene is professionally treated. Halitosis can also be chronic. The causes of chronic halitosis are numerous. They range from chronic infections (e.g., sinusitis) to underlying medical conditions (e.g., uncontrolled diabetes, lung disease, kidney disease). It is estimated that 90 million people have chronic halitosis, according to the Academy of General Dentistry.

When a person believes he or she has halitosis, but the odor cannot be detected by anyone else, it may be a case of pseudohalitosis, which may indicate a psychological problem.