Why does my breath smell fruity or like acetone?

When your body runs short of usable glucose, the liver breaks down fat and makes ketones. One of them, acetone, is volatile, so some of it leaves through your lungs every time you breathe out. That is the smell people describe as fruity, sweet, solvent-like or like nail polish remover. The NHS describes DKA breath as smelling "like pear drop sweets or nail polish remover".

The key point: acetone breath comes from your bloodstream, not from your teeth or tongue. Brushing, mouthwash or tongue cleaning cannot remove it, and masking it can hide a warning sign. Fruity breath and acetone breath are the same thing described two ways, so this page covers both searches.

• A very low-carb or ketogenic diet. Cutting carbohydrates hard pushes the body into ketosis. Cleveland Clinic lists bad breath as a possible side effect and notes that ketosis itself is not harmful. Our keto breath guide covers this in detail.
• Fasting, skipped meals or crash dieting. Going without food depletes glucose stores the same way. The NHS lists fasting and crash dieting among causes of bad breath.
• Diabetic ketoacidosis (DKA). In DKA the body has too little insulin, ketones build up fast and the blood becomes acidic. It mainly affects people with type 1 diabetes, but can occur in type 2 diabetes in people who need insulin.
• Undiagnosed type 1 diabetes. DKA can be the first sign that someone has diabetes at all, particularly in children, according to the NHS and Cleveland Clinic.
• DKA with near-normal blood sugar. Cleveland Clinic notes a less common form, euglycemic DKA, where blood sugar is below 250 mg/dL. Certain diabetes medicines called SGLT2 inhibitors are among the listed risk factors, so a normal glucose reading does not rule DKA out.

The smell alone cannot tell you which one you have. How you feel, and whether you have diabetes, matters far more than how strong the odor is.

If you have diabetes, check your ketones and glucose the way your care team taught you and follow your sick-day plan. The NHS advises calling emergency services or going to the emergency department if blood ketones are over 3 mmol/L, if you cannot check but have DKA symptoms, or if you have DKA symptoms and have never been diagnosed with diabetes. Lower but raised ketones, or high glucose that is not coming down with your usual insulin, need urgent advice from your diabetes team the same day.

If you do not have diabetes and feel well, fruity breath during fasting or low-carb eating is expected. Drinking water and eating regular meals that include some carbohydrate usually makes it fade. If you feel unwell, very thirsty or are peeing much more than usual, get checked, because those can be early signs of diabetes.

Do not drive yourself if you suspect DKA. Ask someone to take you or call an ambulance.

DKA is treated in hospital. MedlinePlus explains that treatment includes insulin, fluids and other care to correct the chemistry of the blood, followed by finding and treating whatever triggered it, such as an infection or missed insulin. Untreated, DKA can lead to complications including swelling of the brain, cardiac arrest and kidney failure, which is why speed matters more than certainty. Going in and being told it is mild ketosis is a far better outcome than waiting at home.

Cleveland Clinic lists missed insulin doses, insulin pump problems, insulin that has expired or been damaged by heat, infections, illness with vomiting, surgery, pregnancy, heavy alcohol use and some medicines (including SGLT2 inhibitors, corticosteroids and some antipsychotics) as triggers. Children whose type 1 diabetes has not yet been diagnosed are a group parents should know about: fruity breath with weight loss, thirst and frequent urination or bedwetting in a child needs prompt medical attention.

We sell tongue scrapers, and we will say it plainly: they do nothing for acetone breath. The smell is exhaled from the lungs. If your breath has both a fruity note and a stale, sulfur-like note, the second part may be ordinary tongue-coating odor, which is a separate issue covered in our guide to bad breath causes. Never try to cover a fruity smell when you also feel unwell.