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Keto Breath: The Unfortunate Side Effect of a Low-Carb Diet

Alexa Rose
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You're totally rocking your new diet, but there's just one problem… your breath smells weird!

Keto breath or “ketotic” breath happens when you are on the ketogenic diet and your body has entered a process of energy generation called ketosis.

What does keto breath smell like? Typically, your bad breath will smell a bit like nail polish and you may also have a sweet taste in the mouth.

While this odd side effect is generally a sign of keto success, acetone breath is hardly a crowd-pleaser. So let's get into it:

  • What is that ketosis smell?
  • How can you make sure it doesn't offend you, your colleagues, or your lovers?
  • How is it different than halitosis?

What is keto?

The ketogenic (keto) diet is a high-fat, low-carb, moderate-protein diet created to help the body achieve a state of ketosis. Ketosis is when the body begins to use the fatty acids and ketone bodies stored in your fat reserves for energy instead of the converted glucose from ingested carbohydrates.

This method has been championed by a lot of celebrities as the diet of the new generation. While the idea of dropping carb intake almost completely may seem in line with older diet methods, the increase of fats intake (60-80% of total calories) may seem less intuitive.

But many claim dramatic results. It certainly does sound a bit extreme, but you can have a brief look at some of the pros and cons of this diet below.



Weight loss

Low-carb diet may not be good for athletes

Good for low activity lifestyle

May not be neough sugar to function properly

May help prevent cancer

High fat diet may be bad for heart

Increased energy

Keto breath

That brings us to our next question: How do you know if you're in ketosis?

Signs you're in ketosis

Ketosis breath
Keto diet helps the body to burn fat reserves.
  • Weight loss: The process of ketosis will have your body burning fats instead of carb-based glucose supply. This can cause the body to noticeably drop weight.
  • Ketone increase in blood: Yes, you can test for ketones in your blood. A hallmark of the keto diet is the increase in blood ketones and the decrease in blood sugar.
  • Increased ketones in breath and urine: Bad breath ( or keto breath) is an unfortunate result of ketosis. When the body burns fat, a substance called a ketone is produced as a byproduct. Ketones are elevated as the body breaks down fatty stores to use for energy in the absence of glucose from carbohydrates. Ketone breath, or when your breath smells like acetone is one way for ketones to be released from the body, urine is the other way that ketones can be passed.
  • Increased focus: Long term ‘ketoers' often report an increase in focus and energy. This is because ketones are an extremely effective fuel source for the brain. A low-carb diet will also stabilize blood sugar levels and this can result in improved brain function.
  • Dry mouth: Having a dry mouth on the keto diet is normal because your system is losing water and electrolytes quickly. Especially if you get rid of all processed foods that you were eating (all the sodium). Rest assured that keto dry mouth can be solved by drinking a lot of water and electrolytes to rehydrate.

Keto breath

So this brings us to our main focus: Keto breath. Keto bad breath is a sign that the body has entered ketosis. Some people report a signature keto metallic taste or a sweet taste in the mouth that is very different from the bad breath resulting from halitosis.

sweet taste in mouth from keto diet
The keto diet can cause foul smelling breath.

It is a common misconception that the bad breath associated with keto is purely from the dry mouth keto diets sometimes cause, although this can certainly cause problems too.

Normally, the body will use carbohydrates to generate glucose for energy. The keto diet helps to get rid of excess fats by starving the body of glucose from carbohydrates, therefore pushing your system to burn up fat reserves.

When the reserves are eliminated, there is a byproduct that needs to be eliminated from the body called a ketone. Ketones can only be eliminated from the body by breath and urine. The keto diet bad breath is a result of ketones leaving the body.

This infographic from SmartMouth sums up what's going on in your body when you embark on this diet:

what causes keto breath

Not everyone experiences bad breath while following the keto diet. You may notice the bad breath at the beginning of your diet but the problem will subside as you adjust to the lower carb intake.

However, when it does occur, the smell can be so offensive that some may seek medical advice on how to prevent it. The good news is that keto breath should only last for a few weeks.

Keto breath test

Having bad breath is embarrassing, especially when you don't notice that you have it. Ignoring a dry mouth on keto is doable, but ignoring the foul odor is more of a challenge. Luckily, there are breathalyzers sold that test the levels of ketones in your breath to help determine if one is in a state of using up fatty reserves.

These breath tests can also help to solve the mystery of why your breath may not be smelling so fresh. The higher the ketone count, the more likely it is that your mouth will smell like a nail salon.

Solutions to keto breath

metallic taste in mouth
Breath spray for keto
  • Eat more carbs: Increasing the number of carbohydrates you eat will pull your system out of ketotic state and eliminate the ketones that are causing the foul odor.
  • Keto breath mints and keto gum: The diet doesn't allow for processed sugar, but there are brands of gum and mints that are keto-friendly that can help mask the temporary bad odor. Some good options are Pur gum and Spry peppermints.
  • Practice good oral hygiene: Brushing your teeth thoroughly and often can help reduce the foul odor from ketogenic processes. Read our guide on best practices.
  • Invest in a good mouthwash: A strong mouthwash will help mask any odor, and there are plenty of varieties to choose from – even if you're not a fan of mint. Our best mouthwash guide has some suggestions, or look at some homemade mouth rinses.
  • Try a breath spray: This one from Dr. Brite features natural and organic ingredients and gives breath a cool minty freshness. Get 10% off with code DRBRITE10.
  • Increase water intake: Drinking more water will help to eliminate the odor caused by a dry mouth and help to stave off the foul odor resulting from ketones.


Keto breath is an unfortunate effect of properly maintaining a state of ketosis. This acetone scented breath is a result of the high amount of ketones in your system from the burning of fat reserves instead of processing glucose for energy. The foul smell isn't a sign of bad bacteria, but rather a sign of a system that has successfully achieved ketosis.

Of course, you should always speak to a doctor before starting any diet, and if you suspect your bad breath is more than just keto breath, you can always consult your dentist.


How long does keto breath last?

Thankfully, it doesn't last forever. Keto breath is most prominent when you first start achieving ketosis, and usually only lasts a few weeks while your system is going through ketosis.

What is keto breath?

Keto breath is the result of a high fat diet. Specifically, it is the smell of acetone resulting from the production of ketones as a by-product of the conversion of stored fat to energy.

Is keto breath a good sign?

Keto breath is the result of successful ketosis in the body. When fat reserves are used for energy the by-product is ketones, which are eliminated from the system through breath and urine.

Keto Breath: The Unfortunate Side Effect of a Low-Carb Diet
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Mayo Clinic: Keto Diet. Accessed 15, June 2020.

American Dental Association: Bad Breath: 6 Causes (and 6 Solutions). Accessed 15, June 2020.