Waking up with the unpleasant hum of dog breath is far from uncommon. Whether it is the after-effects of a curry, or a more lingering problem of sewer-scented oral odour, around 95 per cent of Britons suffer bad breath at some time in their lives. Such is the social embarrassment that £350 million a year is spent on products that promise to sweeten breath. But is it money well spent? An increasing number of medical experts think not, with some going as far as to caution that swilling with a mouthwash can cause more problems than it purports to cure.

Central to the debate about the efficacy of mouthwashes is that many contain exceptionally high levels of alcohol. Some varieties - such as the UK's bestselling brand Listerine - contain 26.9 per cent alcohol, double the amount in wine and more than five times that in beer. It is not just that the alcohol in these products is risky to young children who might get hold of them. According to some critics, it may also render a mouthwash useless. Alcohol can dry out the mouth by drawing moisture from the tissues and slowing the flow of saliva. With limited saliva to flush away or dilute bacteria, it is suggested that rinses that contain alcohol cause germs to become more, not less, concentrated in the mouth - making smelly breath possibly worse.

Dr Philip Stemmer, a dentist who runs the Fresh Breath Centre in London, says that “no mouthwash is a cure for bad breath” - and that “anything that dries the mouth, including alcohol, has the potential to contribute to odours”.

There are many causes of bad breath, he says, including smoking, low-carbohydrate/high-protein diets, which trigger the release of pungent ketones that result in tell-tale dieter's breath, and eating spicy and strong-smelling food - onions, curry etc - that can temporarily make breath smell until the body has digested and eliminated the food.

But the most common reason for offensive mouth odour of the chronic variety is poor oral hygiene. “Bad breath is typically the result of bacteria from particles of food in the mouth releasing sulphur compounds that smell awful,” Stemmer says. “It gets trapped in badly fitted fillings and crowns, cavities and swollen gums and buries itself in the tongue, cheeks and pallate.” A mouthwash, he says, may help to destroy some of the bacteria, but unless they are physically removed through regular, twice-daily brushing - of the teeth and tongue - and flossing, they will thrive and begin to smell. Experts seem pretty unanimous in their view that a mouthwash alone is not the answer.

“It will mask the problem but not necessarily solve it,” says Dr Nigel Carter, of the British Dental Health Foundation (BDHF). Professor Damien Walmsley, scientific adviser to the British Dental Association (BDA), says that the first step for anyone with chronic bad breath is to visit their dentist, who will recommend a good oral cleansing routine that includes the use of a fluoride toothpaste and treatment for any underlying problems. A mouthwash may or may not be recommended. “There is no evidence that alcohol-based mouthwashes are more or less effective,” Walmsley says. “But if you use one, it is probably wise to go for a mouthwash that doesn't contain alcohol.”

Unsurprisingly, the manufacturers of Listerine, Johnson & Johnson, dismiss as poppycock suggestions that its product dries out the mouth. The company claims that more than 30 studies have proven Listerine's effectiveness and points in particular, to one conducted at the State University of New York which showed that even when people with already dry mouths used Listerine three times a day, it didn't make their mouths any drier.

“It is a matter of opinion as to whether alcohol in mouthwashes is a drying agent,” says James Walmsley, medical director of Johnson & Johnson UK. “We don't believe that it is and have evidence to prove that and any mouthwash increases, rather than decreases, salivary rate.”

Alcohol is added not to kill germs, say Johnson & Johnson's representatives, but to act as a carrier for the essential oils menthol, eucalyptol, methyl salicylate and thymol that are the active ingredients in the mouthwash.

“It is there to dissolve these four essential oils,” explains Dr Roberto Labella, associate director of professional and clinical affairs for Johnson & Johnson UK. “Without alcohol, Listerine would lose the efficacy that has been proven in multiple scientific studies and trials and the active ingredients would not penetrate plaque as efficiently.”

Stemmer disagrees, arguing that “there is absolutely no need to put alcohol in a mouthwash and there are effective products out there that contain none”.

But there are not just doubts about the efficacy of alcohol-based mouthwashes. Cancer Research UK is aware of concerns about a possible link between oral cancer and the regular use of high-alcoholic content mouthwashes.

Although there is no conclusive association and “further studies need to be carried out”, the charity's advice is that “the avoidance of high-alcoholic mouthwashes seems prudent”.

With alcohol the second major risk factor for the disease - up to 80 per cent of patients consume it regularly, Cancer Research UK points out - Stemmer says it follows that using products containing high amounts is inadvisable.

Manufacturers argue that the alcohol in mouthwashes is not consumed, merely gargled before being spat out. Is that enough to cause damage? “When you drink a glass of wine, it is in the mouth for a second or two with each sip,” Stemmer argues. “Labels of some products recommend sloshing mouthwashes around in the mouth for 30 seconds to a minute, which means there is a more prolonged exposure to the offending substance, which can't be good.”

So potent are some products that mouthwash abuse is increasingly common among alcoholics - not only does it contain as much as 27 per cent alcohol, compared with about 12 per cent for a typical bottle of wine, but it is cheap and widely available.

In Boston the most stolen item from shops is alcohol mouthwash, prompting many stores to keep it behind the counter. Health officials and charity volunteers in the city say that they have seen an increase in the abuse of mouthwash by homeless alcoholics in recent years, especially when stores selling alcohol are closed.

Both the American Dental Association and the BDHF say mouthwashes are unnecessary and the the latter has associated risks with the alcohol version.

There have been isolated cases, too, of motorists in the UK being found to be “over the limit” after consuming an excess of mouthwash. One man who was breathalysed in Staffordshire a few years ago blamed his addiction to mouthwash as the reason police registered 94 micrograms of alcohol in 100ml of his breath - almost three times the legal limit.

Stemmer believes that excessive alcohol “is completely unnecessary in a mouthwash” and says there are simple steps to cure what can be a psychologically traumatic condition.

“There is no doubt that having bad breath is extremely stressful for some people, to the point where some have committed suicide as a direct result of the problem,” he says. “Treatment will differ according to the cause and some people may need antibiotics to get rid of stubborn bacteria. But halitosis is 98 per cent curable.” And often no mouthwash at all is required.

How to avoid bad breath

1. Allergies and food intolerances can cause bad breath. People with lactose intolerance, for instance, often have smelly breath after drinking milk as a result of an overload of proteins in their mouth

2. Treating sinus problems or a nasal drip can cure bad breath in some cases

3. Although many people think halitosis comes from the stomach, it is rare unless you suffer from excess stomach acid or another clinical problem, in which case you should ask your GP for appropriate medication

4. Brush with a fluoride paste and use unscented floss so that you can detect areas between the teeth that give off odours

5. Drink fluids regularly to promote salivary flow

6. Scrape or brush your tongue to remove bacteria

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