Many people include a daily swill of mouthwash in their dental routine to freshen breath and fight plaque — but could we be damaging our teeth in the process?

Some of the ingredients in mouthwash may have a detrimental effect on teeth and gums if the product isn't used properly, says Robin Seymour, professor of restorative dentistry at Newcastle University.

Many mouthwashes contain alcohol — some are up to 26 per cent proof, research has shown. It's used as a carrier agent, to allow ingredients such as menthol, eucalyptol and thymol to function — these help to penetrate and break down plaque.

But alcohol can cause dryness in the mouth, breaking down the mucus-like coating that keeps the mouth moist. This can lead to bad breath and, Professor Seymour says, cause an uncomfortable stinging sensation in the mouth.

The cancer link

Alcohol-based mouthwash has also been linked to oral cancer. Scientists in a study published in the Dental Journal of Australia in 2009 reported that the ethanol (alcohol) in mouthwash allowed cancer-causing substances such as nicotine to permeate the lining of the mouth more easily. A toxic breakdown product of alcohol called acetaldehyde can also accumulate in the mouth.

Some ingredients in toothpaste, such as the foaming agent sodium lauryl sulphate, can interact with the fluoride in mouthwash, and deactivate it so that it loses its effect. For this reason, wait at least half an hour after brushing before sluicing with mouthwash.

Some mouthwashes can even cause staining. This is due to a chemical called chlorhexidine gluconate — an antiseptic designed to reduce bacteria and remove plaque, both of which can lead to bad breath.

However, when regularly exposed to the teeth it can cause brown patches on the enamel because of a chemical reaction.

"Chlorohexidine can produce tooth staining within ten days of usage because it reacts with food additives which may be left on the teeth, particularly tannins, found in soft drinks, tea and coffee," Professor Seymour says.

So should we just avoid these products altogether? According to Professor Damien Walmsley, scientific adviser to the British Dental Association, it's always worth asking the advice of a dentist.

Guard against decay

London-based dentist Dr Ogo Eze agrees: "If, for example, someone has gingivitis — inflammation of the gums — then it is important to keep plaque levels down, as this can make the inflammation worse. The dentist may suggest a two-week course of a high-fluoride mouthwash to reduce the risk of further decay. There is also a condition called acute necrotising ulcerative gingivitis, which is an acute infection of the gums.

If you don't have any dental problems, Professor Seymour suggests using an alcohol-free brand such as Oral B Anti-Plaque Alcohol-Free Mouth Rinse.

"It doesn't matter how minute the risk of oral cancer might be. It is such a significant disease that there is no reason to take the risk of using a mouthwash that contains alcohol."

To avoid staining, he suggests products such as Dentyl ph, which contain cetylpyridinium chloride (CPC) rather than chlorhexidine — both chemicals act as an antiseptic, but CPC won't stain.

But the British Dental Health Foundation recently reviewed all the evidence about the use of alcohol in mouthwashes and concluded that there is no evidence of a link between mouth cancer and alcohol in mouthwashes.