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Can you smell ketones?


Ketones are chemicals produced when your body breaks down fat for energy. This process occurs when there is not enough insulin to allow glucose to enter your cells for energy. Ketones are formed in the liver and released into the bloodstream. The three main ketone bodies are acetone, acetoacetic acid, and beta-hydroxybutyric acid. Ketosis refers to having elevated levels of ketones in the blood or urine. This can occur during starvation, fasting, low-carbohydrate diets, prolonged intense exercise, and untreated type 1 diabetes. Some people believe they can smell the presence of ketones, usually describing it as a sweet, fruity odor. But is this really possible?

What causes ketone production?

Your body’s preferred energy source is glucose, which mainly comes from carbohydrates. Insulin allows cells to take in and use glucose from the bloodstream. When glucose levels become depleted, insulin levels fall and fat cells release fatty acids. The liver converts these fatty acids into ketones, which can be used for fuel when glucose is unavailable.

Ketones form when:

  • You follow a very low-carbohydrate, high-fat ketogenic diet
  • You fast or eat very few calories per day
  • You engage in prolonged intense exercise without consuming carbs
  • You have untreated type 1 diabetes

In these situations, ketone levels can become elevated. Nutritional ketosis during a ketogenic diet generally produces lower ketone levels than ketoacidosis from diabetes.

Can you smell ketones?

One of the ketone bodies produced in the liver is acetone. A small percentage of acetone is excreted unchanged through urine and breath. Acetone has a sweet, fruity odor that is similar to overripe apples or nail polish remover.

So theoretically, it is possible to smell acetone on someone’s breath if their ketone levels are very high. However, the ability to detect this smell can vary greatly between individuals.

Factors that influence ketone smell detection

  • Ketone concentration – Higher ketone levels make it more likely to produce a detectable smell.
  • Individual olfactory senses – The sensitivity of smell and ability to detect acetone varies between people.
  • Masking odors – Strong smells like coffee breath can cover up the subtle fruity scent.
  • Respiration patterns – Deep breathing through the mouth releases more acetone.

So while it is possible for some people to smell high ketone levels, many are unable to detect this scent. Lack of odor does not mean ketosis is not taking place.

When are ketone levels high enough to produce a smell?

Nutritional ketosis from a ketogenic diet generally produces lower ketone levels, ranging from 0.5-3.0 mmol/L in blood tests. It is unlikely these concentrations are adequate to produce a strong body odor.

Higher ketone levels are found in:

  • Prolonged fasting – After 2 or more weeks of fasting, ketone levels can reach 8-10 mmol/L.
  • Ketoacidosis – In untreated diabetes, blood ketones can reach 15-25 mmol/L.

At these higher concentrations, the acetone odor on the breath may be more noticeable to some people. Untreated ketoacidosis requires emergency medical care.

Ketone level at which odor may occur:

Ketone Testing Method Level Where Odor May Occur
Blood BHB Over 3-5 mmol/L
Breath Acetone Over 1.5-2.0 mmol/L
Urine Acetoacetate Over 40-60 mg/dL

But keep in mind not everyone can smell ketones at these levels. The odor threshold varies substantially between individuals.

When ketone smell is a warning sign

In someone with diabetes, the sweet, fruity odor of ketones can be a warning sign of diabetic ketoacidosis (DKA). DKA is a life-threatening complication requiring emergency treatment. Symptoms may include:

  • Fruity breath odor
  • Nausea, vomiting
  • Stomach pain
  • Shortness of breath
  • Confusion
  • Unusual fatigue
  • Dry mouth

In this situation, the ketone smell on the breath would be very concerning. Prompt medical help is needed to prevent diabetic coma or death.

Should you worry about smelling ketones?

Smelling ketones only indicates your body is burning fat for fuel. It does not necessarily imply something is wrong.

During nutritional ketosis on a low-carb diet, having mild to moderate ketone odors is normal and not dangerous. It simply suggests your body has adapted to using fat instead of carbs for energy.

However, very high ketone levels resulting in a strong odor can occur in uncontrolled diabetes. This ketone smell requires urgent medical care.

In non-diabetic people without health conditions, moderate ketone odors are not harmful. Some may consider it a sign of successful fat burning. But the inability to smell ketones does not mean you are not in ketosis.

Tracking ketones more reliably

Waiting to smell ketones is not the most reliable tracking method. More accurate options to monitor your state of ketosis include:

  • Blood ketone meters – Measure BHB levels with a fingerstick.
  • Urine test strips – Detect acetoacetate in urine.
  • Breath analyzers – Quantify acetone levels in breath.

These devices give you a measurable number, instead of relying on the subjective detectability of odors.

For people with diabetes prone to ketoacidosis, blood ketone testing is recommended for detecting dangerous rises in ketones.

Other causes of fruity odors

While acetone is one source of fruity smells, it is not the only cause. Other conditions can also produce sweet, strong scents:

  • Fruit flavored gum or candy – Chewing fruit gum can give the breath a sweet smell.
  • Phenylketonuria (PKU) – Genetic disorder causing high phenylalanine.
  • Maple syrup urine disease – Metabolic disorder leading to buildup of branched-chain amino acids.
  • Tyrosinemia – Rare genetic disorder affecting tyrosine metabolism.

Discerning occasional ketone odors from other sources can be challenging. Measuring blood or breath ketone levels provides more definitive answers.

Masking ketone odors on the breath

Some people dislike the distinctive fruity aroma of ketones, especially when fasting or first transitioning to a ketogenic diet. Here are some tips to help mask ketone breath:

  • Brush teeth and use mouthwash frequently
  • Chew mint gum or suck on mints
  • Drink through a straw to minimize exhaled breath
  • Use essential oils – peppermint and citrus oils can overpower odors
  • Avoid high protein intake – meat digestion can worsen odor
  • Try activated charcoal capsules – may help absorb some odor compounds

Keep in mind that masking bad breath does not eliminate the underlying cause – the ketones. But these tips can help reduce annoyance from ketone odors.

Conclusion

It is possible in some cases to smell the presence of acetone ketones on someone’s breath. However, the ability to detect this scent varies substantially between people and depends on the ketone concentration.

Nutritional ketosis generally does not produce a strong odor except after an extended fasting period. Very high uncontrolled ketone levels can indicate ketoacidosis, which requires urgent medical treatment in diabetes.

While some view fruity ketone smells as an indicator of fat burning, it is not a foolproof method. More reliable ways to monitor ketosis include testing blood, breath, or urine. An inability to smell ketones does not mean they are absent.