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There is a curse that has plagued humanity[br]since ancient times.

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The Greeks fought it by chewing[br]aromatic resins,

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while the Chinese resorted to egg shells.

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In the Ancient Jewish Talmud,

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it's even considered [br]legal grounds for divorce.

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This horrible scourge is halitosis,[br]otherwise known as bad breath.

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But what causes it[br]and why is it so universally terrifying?

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Well, think of some of the worse [br]odors you can imagine,

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like garbage, feces or rotting meat.

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All of these smells come from the activity[br]of microorganisms,

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particularly bacteria,

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and as disgusting as it may sound,

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similar bacteria live in the moisture-rich[br]environment of your mouth.

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Don't panic.

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The presence of bacteria in your body[br]is not only normal,

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it's actually vital [br]for all sorts of things,

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like digestion and disease prevention.

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But like all living things,[br]bacteria need to eat.

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The bacteria in your mouth [br]feed off of mucous,

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food reminants,

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and dead tissue cells.

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In order to absorb nutrients[br]through their cell membranes,

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they must break down the organic matter[br]into much smaller molecules.

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For example, they'll break proteins [br]into their component amino acids

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and then break those down even further[br]into various compounds.

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Some of the foul-smelling [br]byproducts of these reactions,

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such as hydrogen sulfide and cadaverine,

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escape into the air

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and waft their way [br]towards unsuspecting noses.

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Our sensitivity to these odors[br]and interpretation of them as bad smells

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may be an evolutionary mechanism[br]warning us of rotten food

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and the presence of disease.

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Smell is one of our most intimate[br]and primal senses,

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playing a huge role [br]in our attraction to potential mates.

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In one poll, 59% of men and 70% of women

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said they wouldn't go on a date [br]with someone who has bad breath,

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which may be why Americans alone

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spend $1 billion a year [br]on various breath products.

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Fortunately, most bad breath [br]is easily treated.

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The worst smelling byproducts come from[br]gram-negative bacteria

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that live in the spaces [br]between gums and teeth

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and on the back of the tounge.

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By brushing and flossing our teeth,

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using antibacterial mouthwash at bedtime,

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gently cleaning the back of the tongue[br]with a plastic scraper

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and even just eating a healthy breakfast,

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we can remove many of these bacteria[br]and their food sources.

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In some cases, [br]these measures may not be enough

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due to dental problems, [br]nasal conditions, or rarer ailments,

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such as liver disease [br]and uncontrolled diabetes.

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Behaviors like smoking [br]and excessive alcohol consumption

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also have a very recognizable odor.

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Regardless of cause,

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the bad smell almost [br]always originates in the mouth

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and not the stomach [br]or elsewhere in the body.

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But one of the biggest challenges lies

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in actually determining [br]how our breath smells in the first place,

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and it's unclear why.

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It may be that [br]we're too acclimatized

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to the smell inside [br]our own mouths to judge it.

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And methods like cupping your hands[br]over your mouth,

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or licking and smelling your wrist[br]don't work perfectly either.

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One study showed [br]that even when people do this,

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they tend to rate the smell subjectively

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according to how bad [br]they thought it was going to be.

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But there's one simple,[br]if socially difficult,

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way of finding out how your breath smells:

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just take a deep breath and ask a friend.