It's the hidden health problem that affects nearly half the population and raises the risk of snoring.

But experts say that people who mouth-breathe have much more to worry about than disgruntled partners being woken up by their snores.

Experts argue that growing research shows that the habit, characterised by the tendency to breathe through the mouth instead of the nose, disrupts sleep, and can trigger serious, even life-threatening, health problems.

'Long-term mouth breathing can have negative health impacts,' says Professor Adam Taylor, an anatomy researcher at the University of Lancaster.

'This ranges from heart disease to bad breath and fatigue.'

Research suggests mouth-breathing could also raise the risk of obesity, dementia, arthritis and even some forms of cancer.

However, experts argue that patients can fix their mouth-breathing without the help of a doctor.

Estimates on the number of people who are mouth-breathers vary. However, according to sleep expert James Nestor, who wrote the bestseller Breathe, as many as half of the population are affected.

Experts say that no one breathes through their nose 100 per cent of the time, however, normally this is only for short periods when the body is at stress such as during exercise, rather than during sleep or when resting.

Research suggests there are two reasons why patients might mouth-breathe.

'There are those whose chronic mouth-breathing is caused by structural issues in their nose such as a deviated septum, a nasal obstruction or polyps,' says Dr Dan Baumgardt, a GP and researcher at the University of Bristol.

'But you also have patients who have become chronic mouth-breathers out of habit.' 

Dr Baumgardt argues that many patients may not realise they mouth-breathe, and adds that patients should look out for several symptoms.  

'Patients are often tired during the day, triggered by a lack of sleep,' he says. 

'Poor oral hygiene like bad breath, an intense thirst and partners complaining of snoring are also signs of mouth-breathing.'

Experts say one of the main reasons why the habit is dangerous is because it dries out the mouth, creating conditions in which harmful bacteria can grow.

Growing research shows that bad oral health can raise the risk of diseases including heart disease, stroke, rheumatoid arthritis and even colon cancer.

‘We can tell when a patient comes in and they are a mouth-breather - they will have inflamed gums in their front teeth and recurrent dry mouth,’ says Dr Victoria Sampson, a dentist and specialist in the oral microbiome.

‘Mouth-breathing results in less saliva being produced which helps to balance the environment, so without it a mouth will host more bad bacteria.

‘This is a problem as we know that this bacteria is linked to a range of health problems such as gum disease and increased risk of cardiovascular disease.’

Another reason mouth-breathers are at-risk, according to experts, is because they are missing out on the body's natural defences against harmful pathogens. 

'The nose has a number of structural elements which makes breathing through it beneficial,' says Professor Taylor.

'The nose hairs filter out harmful particulates, but it also moistens air and heats it so it is perfect for the lungs to be able to process without having to take big heavy breaths which put strain on the respiratory system.'

Research also suggests that mouth-breathing can disrupt sleep. This is because, when the mouth is open during the night, the tongue and jaw tend to fall backward, partially blocking the airway.

This problem can lead to snoring, pauses in breathing and frequent awakenings during the night. Experts say that, over time, this can lead to poor health, including raising the risk of obesity.

A 2018 Finnish study found that young children who mouth-breathe are more likely to be obese later in life.

In recent years, a number of celebrities have backed the controversial practice of mouth-taping, which many claim can solve mouth-breathing.

It involves covering the lips with adhesive tape, to encourage the body to breathe through the nose instead.

Supporters include Premier League footballer Erling Haaland who has claimed it helps improve his performances on the pitch.

Meanwhile, Strictly Come Dancing departing presenter Tess Daly has said mouth taping gives her 'more restful sleep', and has posted pictures of herself, mouth tape in place, to prove it.

A major review of 177 studies on mouth tape published last year in The American Journal of Otolaryngology found, perhaps surprisingly, no evidence that mouth tape is effective, meaning it neither improves sleep quality nor reduces snoring.

'Mouth tape is not something that should be advocated for,' says Professor Taylor.

'If someone is a chronic mouth-breather they will find a way to do it even with mouth tape on. This may mean they try to force their breath out the sides of the tape, which can lead to a build-up of carbon dioxide in the body sending it into a state of stress.

'There is very limited research to suggest it is effective and for those with structural problems, taping can be dangerous. If you are still tempted to try it opt for a tape that is vertical and a specialist product not gaffer tape style seal.'

For people who struggle to naturally breathe through their noses, experts say one simple daily exercise is significantly more effective than covering the mouth with tape.

According to functional breathing coach Victoria Wilson a technique called alternate nostril breathing can help patients breathe through their mouth less.

Ms Wilson claims that, as well as stress-reduction, improving nasal breathing can decrease blood pressure. 'Firstly, sit in a chair and relax your shoulders,' says Ms Wilson.

'Take your right thumb, put it over your right nostril and breathe in through your left nostril once and then exhale. Then, alternate so that your finger is now covering your left nostril, breathe in through your right nostril and exhale.

'If you repeat this cycle twice a day for at least two cycles and you will begin to see an impact pretty quickly.'

Famous fans of the exercise include former US presidential candidate and First Lady Hillary Clinton, who says she practises alternate nostril breathing every day to reduce her stress levels. 

Alongside the breathing exercises Ms Wilson recommends using a saline nasal solution to help clear the airways, or specialist product like Xlear that she is an ambassador for. 

This is because some patients mouth-breathe because their nasal passages are blocked. 

However, Professor Taylor warns: 'Before patients opt for DIY home fixes they should consult a GP to make sure there is not an underlying structural problem causing their chronic breathing.'