Has a friend or significant other gently hinted that your breath is, um, pungent? (Many halitosis sufferers can't tell.) Brushing and flossing more diligently may do the trick, but a few more minutes at the sink won't always help, say experts. Below are eight causes of bad breath that may surprise you.

Medications

Saliva rinses away bacteria that foul the breath, and many drugs, among them antidepressants, diuretics, and even aspirin, can dry the mouth.

Diet

Foods high in protein or dairy products generate large amounts of amino acids, which are fodder for bacteria. A diet low in carbs burns stored fat, creating toxic-smelling ketones. And last year, researchers linked bad breath with obesity, although the basis is unclear.

Skipping breakfast

Besides the well-established advantages to body and mind of having a good breakfast, it helps quell morning breath by stimulating saliva production and scrubbing bacteria from the tongue. (But lay off the sardine-onion sandwich.)

Alcohol

Heavy alcohol consumption also can dry out the mouth.

Bacteria

The stink-creating kind mostly hang out on the tongue, happily churning out gases as they munch on food particles and substances broken down from saliva. They multiply at night when the salivary glands slow down (hence morning breath). Some people harbor more species of malodorous bacteria than others do, which may be why certain individuals are especially halitosis-prone. This month, a study in the "Journal of Medical Microbiology" suggests that H. pylori, the same bug that is often responsible for stomach ulcers, can cause bad breath and gum disease if it finds a home in the mouth.

Mouth breathing

Any condition that dries the tissues of the mouth, preventing saliva from washing away bacteria, encourages bad breath. Candidates include sleep apnea, snoring and asthma.

Ongoing illnesses

A potent breath can signal particular diseases. Kidney failure produces a fishy smell and uncontrolled diabetes generates fruity fumes, for instance.

Respiratory tract infections

Tooth and gum infections are recognized sources of bad breath. But so are bronchitis, sinusitis and even a cold. RTIs break down tissue, starting a flow of cells and mucus that feed bacteria that create foul odors.