A researcher at the University of the West of England (UWE Bristol) has devoted her work to a subject that some might find unpleasant or embarrassing: bad breath. Over the past two decades, Dr Saliha Saad and colleagues have tried to pinpoint the mechanisms behind oral malodour, also called halitosis, and how best to reduce it.  

A link between the biofilm on our tongue and oral malodour

While bad breath can be the result of eating strong-smelling foods like eggs, a meat morsel caught between the teeth, or gum disease, these lead only to temporary oral malodour. Dr Saad’s research examines more long-lasting, chronic halitosis in people who, despite living a healthy lifestyle with good oral hygiene, experience the symptom on a regular basis.

We humans carry 1.5kg of microbes, also called human microbiota, on the inside and outside of our bodies, found on our skin, in our intestines and in our mouths. At the back of the tongue is a biofilm, a collection of millions of bacteria within a thin, robust protective coating (which the bacteria excrete). Although researchers are still trying to identify all the possible causes of halitosis, they believe this film of microbes is responsible for oral malodour. “Our theory is that the more bacteria on our tongues, the higher the instance of smelly compounds found in our breath,” says Saad.

Through her research with Professor John Greenman, Dr Saad has learned that people with oral malodour may have it their entire lives. As a result, Saad and her team have worked with Colgate Palmolive, Philips, GSK, Procter & Gamble, Healthcare International, Boots, GABA and other oral hygiene companies to help them develop more effective toothpastes, mouthwashes or cleaning devices. “Brushing and flossing can reduce bad breath for a certain amount of time, but the challenge is to cut bad breath for longer. Our job is to show these companies whether their product has a longer lasting effect on oral malodour,” explains Saad.

Testing products that counteract bad breath

To try to achieve this, the researchers test anti-microbial samples the companies send them using a biofilm perfusion system. This involves gently scraping volunteers’ tongues to obtain the collection of microbes, before injecting the resulting liquid onto cellulose, a material that best represents the surface of a tongue. A fluid almost identical to saliva is then slowly drip-fed onto the biofilm to emulate the environment (including pH and temperature) found in a human mouth.

Once the bacteria reaches a steady state, the scientists inject controlled amounts of the unlabelled oral hygiene sample onto the microbes. “These products are invariably a type of toothpaste but we often don’t know what active ingredients they contain,” says Saad. The process of reduction in bacteria and smell is then measured over time.

Following this in vitro testing, the scientists conduct clinical trials by asking some 150 volunteers to test toothpastes or other oral hygiene products such as mouthwashes. The intensity of their malodorous breath is assessed both before and after the treatment using a SIFT-MS machine. The device uses a technique called ion flow-tube mass spectrometry to ‘smell’ the breath by providing a breakdown of the gases contained within it. “Generally the most odorous gases are the sulphides,” explains Saad.

Because machines and other measuring devices can sometimes be inaccurate, Saad herself also smells the volunteers’ breath. As a qualified organoleptic judge, she can categorise the odour by intensity and unpleasantness according to a set technique and scale. The participants are then provided with a toothpaste or mouthwash to test, with Saad checking their breath in the subsequent hours. Test results are subsequently analysed and sent on to the oral hygiene companies concerned.

UWE Bristol is unique in that it provides a course to train scientists to become organoleptic judges with Saad as their trainer. By the end of the five-day course the professionals, who are from all over the world, learn to use the sniffing test to diagnose oral malodour and assess the effects of treatment interventions in their own practices.

As for those who suddenly recognise that they have momentary smelly breath, perhaps just as they are about to walk into an interview, Saad proffers her advice for quick remedy. “Gently brush the back of your tongue,” says Saad. “But be careful not to damage it because if you brush too hard you could cause injury and infection.”

• UWE Bristol research