Why does my breath smell like ammonia or pee?

Healthy kidneys filter urea and other waste out of the blood. When kidney function falls far enough, these substances accumulate, and some, especially ammonia, are exhaled. MedlinePlus lists breath that smells like ammonia or urine, or that smells "fishy", among the signs associated with chronic kidney failure. The Merck Manual describes renal failure breath as smelling of urine or ammonia.

A 2012 breath study in PLoS One found that breath ammonia rose as kidney function declined and fell after dialysis, which supports what clinicians have long noticed at the bedside.

• Advanced chronic kidney disease or kidney failure. The main cause doctors think of. MedlinePlus lists breath odor among symptoms that appear once kidney function has worsened.
• Acute kidney injury. A sudden drop in kidney function, for example during severe illness or dehydration, or from some medicines, can cause the same waste build-up.
• Liver failure. The breath of liver failure is usually described as musty and sweet, but Cleveland Clinic notes ammonia can contribute to it.
• Helicobacter pylori stomach infection. This bacterium makes an enzyme that turns urea into ammonia, and a 2016 meta-analysis found people with H. pylori were more likely to have bad breath. Evidence that it causes a distinctly ammonia-like smell is limited.
• Mouth sources. Ordinary bad breath from the tongue and gums is mostly sulfur, but mixed smells are hard to name, and some people describe stale oral odor as "ammonia".

You may read online that dehydration or a high-protein diet gives ammonia breath. Both can worsen general bad breath, but neither is a recognized cause of true uremic fetor, so do not let them explain away a smell that persists.

Early kidney disease usually causes no symptoms at all, which is why breath changes tend to appear late. NIDDK lists these signs as kidney function falls:

• Swelling in the legs, feet or ankles
• Itchy skin, headaches, tiredness and poor sleep
• Feeling sick, losing your appetite or sense of taste, weight loss
• Making little or no urine
• Muscle cramps, weakness or numbness
• Confusion, trouble focusing or memory problems

Many people with kidney disease also notice food tastes different or metallic. See our page on metallic taste.

A doctor will usually ask about your symptoms and medicines, check your blood pressure, and order a blood test for kidney function and a urine test. These are routine, fast and the only way to know whether the kidneys are involved. If you already have kidney disease, tell your kidney team about a new ammonia smell or taste change, because it can reflect how well waste is being cleared.

Keep brushing, flossing and drinking water as your doctor allows, since a dry mouth makes any odor stronger and people with kidney disease are sometimes asked to limit fluids. Sugar-free gum can help with an unpleasant taste. But no mouth product removes a smell that comes from the blood, so treat home measures as comfort, not as a fix, and book the tests.