Robert Brown|Bad breath is common but preventable. Here's what causes it.

Few things are Robert Brownas off-putting as having bad breath. We inwardly cringe or turn away when a friend or coworker has stinky breath, and identifying an unpleasant odor coming out of one's own mouth in social gatherings can be embarrassing and even lead to anxiety about being around others. 

"No one wants bad breath and face-to-face interactions are simply more pleasant when it's been properly taken care of," says Kasandra Heath, a registered dental hygienist at Mesa View Dental in St. George, Utah. 

But not wanting bad breath and understanding what causes it are two different things. Here's what's behind unpleasant mouth odor - and how to prevent it. 

What is halitosis? 

Though some people think of halitosis and bad breath as being two different things, "they are actually one in the same," says Dr. Christopher Pullins, a family medicine physician at Mayo Clinic. 

Indeed, as the official medical name for mouth odor, "halitosis" is actually Latin for "bad breath." Though we often think of bad breath as being temporary, "halitosis can also be chronic," explains Dr. Mirissa Price, an expert spokesperson for the American Dental Association and a pediatric dentist at Boston Children’s Hospital. 

It's also not uncommon. "Studies show that 50 percent of adults have had bad breath, or halitosis, at some point in their lives," she says. 

What are the symptoms of bad breath?

While the most obvious symptom of bad breath is, well, bad breath, there are other symptoms one can watch for. These include a white coating on the tongue, a dry mouth, or excess mucus entering the back of the throat from one's nose or sinuses - usually stemming from nasal irritation, allergies, or a bacterial infection. "This is called a post-nasal drip and often accompanies mouth odor," says Heath. 

And because bad breath is often associated with tooth decay, plaque buildup around one's teeth can be another sign to look out for. "Persistent bad breath can be a warning sign of gum disease, which is caused by genetics, leftover plaque, or both," says Price. 

It's worth noting that gum disease and post-nasal drips can be either symptoms or causes of mouth odor. 

What causes bad breath? 

Another cause of bad breath is eating stinky or spicy foods such as onions, tuna, flavored potato chips, chilies, beef jerky, horseradish, and garlic. "Smoking can also contribute to bad breath," says Pullins. 

Dry mouth causes stinky breath as well. It stems from a lack of saliva, and saliva has the important job of keeping the mouth clean. "Dry mouth can have many causes, such as medications, salivary gland problems or mouth breathing," explains Price. Indeed, decreased saliva production at night or a drying out of one's mouth due to snoring all night is why many people wake up with what we refer to as "morning breath." 

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But the most common cause of bad breath is the presence of bacteria. "There are hundreds of types of bad breath-causing bacteria living naturally in your mouth," explains Price. "These bacteria grow in your mouth, which acts as a natural hothouse." She explains that mouth bacteria feed on the plaque between teeth and on the leftover food after we've eaten, "which leads to a foul-smelling waste product being left behind."

Heath says that one of the most common places to find an accumulation of these bacteria is on the tongue. "If you fail to clean this surface, the buildup can cause your breath to really stink," she explains.

And while Pullins agrees that "90% of halitosis cases originate from an oral source," he says there are times when smelly breath is also related to gastrointestinal issues like acid reflux or GERD, or due to certain medical conditions such as liver or kidney disease. 

While conditions like these often require additional medical intervention, Price says that bad breath can generally be prevented by staying hydrated and by regularly eliminating bacteria through good oral hygiene. "It's also wise to avoid smoking and to steer clear of the foods that lead to bad breath," she says.