The study of halitosis has, and hasn't, evolved much in a century

Consider bad breath and its causes - gingivitis, tooth decay, pungent foods, smoking, alcohol use and periodontitis - and you might think that research into the complexities of halitosis has advanced by leaps and bounds in the past century or so. On the other hand, you could believe that many key factors behind oral odor were discovered ages ago. In either case, you'd be right.

A little more than 100 years ago, research into halitosis was almost as intense and multifaceted as it is today. Consider an 1896 volume of The Dental Cosmos, which was a monthly journal of dental and craniofacial science founded in the late 1800s.

In an article titled "Foetor ex Ore: Pathology and Therapy," expert H. Jerome Allen runs down the then-current notion of what causes bad breath - or fetor ex ore, as it was commonly known, a Latin phrase meaning "fetid air from the mouth."

Allen, who originally read his article as a speech before the Washington City Dental Society, notes that one of the worst aspects of being a dentist is being exposed to the foul breath of his patients, a suffering that is compounded by the fact that most cases of the condition are "invariably curable."

The oral health expert goes on to list what he believes are the most common causes of bad breath. These include acid reflux, gastrointestinal disturbances, tonsillitis, bronchitis and any condition that "retards the passage of decomposing waste matter through the intestines."

Allen is largely right about catarrh, which is an antiquated term for sinus trouble. Today, most oral hygienists acknowledge that postnasal drip can lead to smelly breath, since the movement of mucus down the back of the throat can tinge one's exhalations with its smell.

The dentist is also correct about the gastrointestinal causes of halitosis, with the possible exception of his delicate reference to constipation. However, he is not accurate when it comes to the matter of degree. While gastric and lung problems can give the breath a foul odor, most "fetor ex ore" originates from where the phrase indicates - the mouth.

The current opinion on bad breath is that more than 90 percent of it is emitted from the palate, gums and tongue. The Encyclopedia of Family Health, published slightly more than a century after Allen's speech, states that the most common causes of halitosis are dental problems, smoking and spicy foods.

The book notes that the condition is relatively simple to treat. Unlike a century ago, individuals today have access to a wealth of specialty breath freshening products, like oral care probiotic kits.

However, one thing has hardly changed in 100 years. As Allen writes in 1896, "such is the universal false kindness of...relatives and friends that, with the best intentions in the world, they would rarely whisper...a word of [your] disorder."