Can they smell the coffee I swigged ten minutes ago? Was my lunch really that garlicky? And why on earth did I choose the cheese and onion crisps? We've all experienced the paranoia that sets in when someone offers you a mint but, according to Harley Street gum specialist and oral health expert Dr Reena Wadia, a post-food whiff isn't the only cause of bad breath. Also known as 'halitosis', one in three of us has bad breath and we may not even know.

"There are many causes of bad breath from 'workout breath' – triggered by dehydration – to the unpleasant breath that's common in crash dieters," Dr Reena says.

"When we were all regularly wearing face masks during the pandemic, many people became more aware of their breath. A quick way to smell your own is to lick the inside of your wrist and wait a few seconds before sniffing it. You may also notice a metallic or unpleasant taste in your mouth but the best way to know for sure is by asking your dental professional," explains Dr Reena who is also the founder of RW Perio, a specialist gum health clinic in London's Marylebone, and host of the Life & Smile podcast.

Dr Harold Katz, dentist, bacteriologist and founder of The Breath Company, suggests wiping the top surface of your tongue with a piece of cotton gauze and looking for a "foul smell or yellow-ish stain." The back of your tongue may also appear whiteish when you look in the mirror.

So, what exactly causes a pong in the first place? "It's the strong-smelling volatile sulphur compounds (VSC) that are released when bacteria, living on the tongue and throat, digests proteins. Saliva is important as the drier the mouth, the more the bacteria can thrive and the more likely you are to suffer from smelly breath," explains Dr Reena.

Tackling bad breath won't just help you score when it comes to dates and job interviews - it could also reduce your risks of developing other conditions further down the line. Gum disease is often behind it – and this is linked to increased risk of heart disease, strokes and even dementia due to the bacteria in the mouth spreading to other parts of the body.

Bad breath has also been linked to COVID-19 since the virus can cause changes to the surface of the tongue and the chemicals in saliva.

Here, we take a look at the biggest bad breath causes and the best ways to counter them...

Cause: "Dehydration is a big cause of bad breath, since your body is unable to produce sufficient saliva. Intense workouts and smoking are common culprits, but there are other surprising causes, too, such as spending the day sitting on a hot beach or during a flight when humidity in the cabin is low," says Dr Reena. And yes, dehydration in a heatwave, or at any other time can make your breath pong.

Fix: She advises steering clear of the booze. "Alcohol will only dehydrate you more while sugary sports drinks or fizzy drinks can cause tooth erosion. Keeping hydrated with plenty of plain water is the best option here."

Cause: If one of his clients is experiencing bad breath, one of the first things nutritionist Daniel O' Shaughnessy asks is whether they are following any drastic diets.

"When someone embarks on an extreme low-carb diet, like the Atkins diet or a ketogenic diet, the body goes into a state called ketosis, where your body uses fat for energy so you burn things called ketones. The release of these chemicals can contribute to bad breath," he explains.

Fix: Oil pulling may have a place in your self-care routine. "It can help cleanse the mouth of plaque build-up and bacteria," he says. After brushing your teeth at night, swish a teaspoon of coconut oil around your mouth for five to 10 minutes and spit it out."But my advice here is to follow a sensible diet. You don't have to go on a low-carb diet to lose weight."

Cause: "In clients with bad breath, I also look at digestive function and whether there are bacterial imbalances in the digestive tract. This could be a bacterial overgrowth from things like Helicobacter pylori (H. Pylori) or small intestinal bacterial overgrowth (SIBO)," Daniel says. "These have other symptoms, too, such as a lot of bloating, especially after eating."

Acid reflux is another gut-related cause of bad breath, Dr Reena points out. Also known as GERD or gastro-oesophageal reflux disease, reflux can cause smells from our stomach, while also making the mouth more acidic.

Fix: Solutions for acid reflux include antacids, that can be taken with food or soon after eating, and reducing triggers such as tomatoes, chocolate and fatty or spicy foods.

If you suspect your bad breath could be caused by an imbalance of bacteria in your digestive tract, Daniel advises getting a test from your doctor or nutritionist. "You can also increase your intake of probiotic foods or probiotic supplements, although they won't make H.Pylori or SIBO disappear, that would require antibiotics from a doctor."

Cause: Intra-oral bad breath is one of the most common types and it refers to anything dental-related, including tongue coating or gum disease.

"Improper oral hygiene can be behind this. Your tongue is like carpet – it's made up of lots of little nooks and crannies and if you don't clean it properly, it's going to smell. Similarly, not cleaning in between your teeth means you're missing out on half the area of your teeth," Dr Reena says.

Fix: She advises cleaning your tongue once a day, after brushing your teeth, using the RW Perio Tongue Scraper, £20. For in-between the teeth, opt for floss or interdental brushes.

Mouthwash is also key, although be sure to use this at a different time to brushing as you don't want to wash away the fluoride from your toothpaste. Dr Reena suggests doing so after lunch.

Dr Katz recommends his The Breath Company Healthy Gums Oral Rinse, £15, since it doesn't contain alcohol which can dry out the mouth further.

Probiotics have also been shown to impact the bacteria in our mouth. A 2006 study found oral probiotic lozenges  significantly reduced those smelly sulphur compounds. The same strains were able to reduce other causes of bad breath, including gingivitis, pharyngitis, oral candidiasis and dental decay.

Try Luvbiotics Advanced Dental Hygiene Lozenges, £8.95 for 30, or Invivo Bio. Me Oral Food Supplement Mouthwash, £31. Invivo also offers an oral microbiome profile kit, £139, that tests for the bacteria that can lead to gum disease.

Cause: Saliva production decreases when we sleep, causing a dry environment that lets bacteria grow, explains Dr Reena. And so-called 'morning breath' tends to be worse in people who sleep with their mouths open.

Fix: Thoroughly cleaning your teeth and tongue before bed will help. The good news is, this is one of the easiest types of smelly breath to banish – simply cleaning your teeth first thing should see it off.

"Brush before you have breakfast. Brushing straight after consuming acidic and erosive food and drink, such as orange juice, can damage the teeth," she adds

Cause: Onion, coffee and garlic are all common offenders when it comes to food-induced bad breath with garlic being the most potent since it also contains allyl methyl sulphide – a molecule that is absorbed into the bloodstream and emitted through our pores.

But there's another hidden culprit, too. Amino acids in dairy products feast on bacteria in your mouth, producing more of those smelly sulphur compounds. "Refined and processed sugars also provide a food source for bacteria. Coffee and juices can contribute to this problem because they are acidic and provide these bacteria with an ideal breeding environment," adds Dr Katz.

Fix: Mints or sugar-free chewing gum are some of the fast-track fixers for this, although Dr Reena advises opting for the latter since it also stimulates saliva production which in turn, helps nuke those smelly sulphur compounds.

Dr Katz recommends munching on apples, celery and carrots. "These work to 'brush' the teeth thanks to their high levels of good starch that rinses away dental plaque," he explains. 

And what about those old wives' tales about chewing fennel seeds or parsley? "Fennel seeds could help temporarily but only by masking the odour –a bit like perfume," offer Dr Reena. There is some truth in the idea of chewing on ginger for bad breath, though. One small study in 2017 found a ginger spray rapidly increased saliva in diabetes patients suffering from dry mouths. A test in 2015 also showed green tea could be beneficial in cases of halitosis.

Cause: "In some cases bad breath is a sign of another disease such as ketoacidosis in diabetes, kidney problems or even liver cirrhosis," says Dr Reena. 

In fact, research suggests an estimated 10 per cent of all halitosis cases are caused by certain illnesses, according to Dr Katz. "Individuals who suffer from lung disease, cancer, respiratory tract infections, HIV, zinc deficiency, or metabolic disorders may often experience bad breath due to dry mouth. Sinusitis, pneumonia, bronchitis, post nasal drip, and polyps affect the airways and may also contribute to the problem, while other conditions associated with bad breath include nasal odour and tonsil stones and yeast infections of the mouth. Certain drugs, too, such as antidepressants, high blood pressure medications, and antihistamines can factor into dry mouth because they reduce saliva production."

Fix: If you think you may have bad breath, contact a dental professional. Once they've eliminated all other causes, they may advise you to see your GP who can help to diagnose any other health problems.

GET MORE GLOSS: Is lymphatic drainage the secret to a longer life and leaner body?

Editors Picks: Things we're loving