Field of Science

Halitosis - Your mouth smells like arse

This post was chosen as an Editor's Selection for ResearchBlogging.orgSometimes I'm going to write about rare cancers or blood diseases and sometimes I’m going to write about bad breath. That’s just the way I roll.

Halitosis literally means “condition of the breath” and has many causes and just as many home remedies. Original therapies (and by original I mean 1550 BC) like heavily herb infused wines didn’t remove the bad breath but like mints and other modern treatments they just attempted to cover the bad smell with something more pleasant.

Halitosis isn't limited to humans. Ever smelt a dogs mouth?
Halitosis can be divided into two distinct problems, transient halitosis (morning breath) and chronic halitosis. While the difference between these conditions is the time frame of affliction both have the same root cause. Sulphur.

A study by Suarez et al. looked at what caused the odour in people with morning breath and found that the unique smells produced by people were due to three sulphurous gases combining into a malodourous mixture. The gases, hydrogen sulphide (smell of rotting eggs), methanethiol (smell of rotting cabbage) and dimethylsulphide (which has a slight sweet smell), were present in varying quantities between participants giving them all bad morning breath.

The sulphurous gases are produced by bacterial build up in the mouth and in particular on the tongue. During the night your production of saliva drops significantly and with less saliva bacterial numbers increase dramatically. Saliva has a number of jobs in the mouth related to bacterial load but its three main roles are to acts as a tidal wave to wash bacteria out of the mouth, to inhibit bacterial growth using various chemical components and participate in the killing of bacteria by carrying parts of the immune system into the mouth. But less saliva equals more bacteria and consequently, bad breath.

Given this it wasn’t surprising that the treatments that Suarez et al. found good immediate treatments of halitosis (I say immediate because as saliva production increased the bad breath went away naturally) where mechanical scraping of the tongue. Specifically brushing of the teeth with toothpaste did nothing but brushing of the tongue with water was much more effective. Eating a dry bread roll was also very effective as it scraped across the tongue, removing bacteria.

The best treatment was a mouthwash of 5mL of 3% hydrogen peroxide – guess why. This treatment killed huge umbers of bacteria and immediately dropped the concentration of the sulphurous gases, which stayed low for hours afterwards.

While rare there are a few conditions that produce halitosis that has a non–oral origin but they are extraordinarily rare and halitosis is but one of a bevy of symptoms that the patient would possess.

Foetor hepaticus, or the ‘breath of the dead’, is seen in people with late stage liver failure. It is caused by the passage of thiols from the blood into the lung. These compounds are normally removed in the liver but as the liver shuts down thiols remain in the blood and can escape into the lungs. Apparently distinct from typical halitosis foetor hepaticus smells of sweet faeces.

Another condition, known as trimethylaminuria is also known as fish odour syndrome. People suffering from trimethylaminuria lack the metabolic enzyme Flavin containing monooxygenase 3 which breaks down trimethylamine to trimethylamine oxide. The result is that trimethylamine builds up in the blood and is removed in the urine, sweat and breath. Despite its name an odour of fish is rare and most sufferers just have an unusually strong and sometimes unpleasant odour.

So if you have halitosis, but don’t have late stage liver failure or metabolic disease, you can treat your bum breath with breakfast and mouthwash if you pedantic. So no excuse for blowing it in my face on the train from now on!

Suarez FL, Furne JK, Springfield J, & Levitt MD (2000). Morning breath odor: influence of treatments on sulfur gases. Journal of dental research, 79 (10), 1773-7 PMID: 11077993


  1. Hi James, another fabulous post. I just like to add that sometimes conditions like lung abscess and tonsillitis can also cause halitosis.

  2. @Debajyoti Awww shucks. Thanks for the kind words and the extra info. I guess I glossed over those and went straight from bacteria to rotting liver :D


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