Smelling urine when it's not there is often phantosmia (olfactory hallucination), where your brain perceives odors not present, commonly due to sinus issues, colds, allergies, or dental problems, but sometimes linked to nerve or brain conditions, COVID-19, or medications; it's usually harmless but see a doctor if it persists to rule out serious underlying causes like nasal polyps or neurological issues, as treatments vary.
Smelly urine or urine that has an unusual odor may be a result of diabetes, an infection, eating asparagus, or using certain medications, among other causes. Treatment can depend on the underlying cause. Urine often has a slight ammonia smell, especially first thing in the morning or when a person is dehydrated.
When the kidneys aren't functioning properly, waste products like urea can build up in the body and produce unusual odors. This is sometimes referred to as “uremic fetor,” a term for the strong ammonia or urine-like smell that may come from the breath or nasal passages in people with kidney problems.
You should worry about urine smell and see a doctor if it's persistent, accompanied by fever, pain/burning during urination, cloudy or bloody urine, or if it smells sweet (potential diabetes) or rotten (potential infection/kidney stones). While often temporary due to dehydration or food, persistent strong or unusual odors, especially with other symptoms, warrant medical attention to rule out UTIs, diabetes, or other conditions.
The main symptom of Trimethylaminuria is a strong odour that may be described as smelling like rotten fish, eggs, rubbish, or urine. The smell is usually noticeable in your sweat, urine, and breath.
Key takeaways:
Foul-smelling urine is not a symptom of cancer. The most common cause of foul-smelling urine is a urinary tract infection.
Kidney failure can make urine smell strongly of ammonia or have a fishy odor, often due to built-up waste products (amines) or infection, signaling concentrated urine from dehydration or kidney dysfunction. Other signs alongside bad-smelling urine include foamy, bloody, or cola-colored urine, swelling, fatigue, and changes in urination, all pointing to potential kidney issues that require a doctor's evaluation.
See a GP if:
You have smelly pee and: you need to pee suddenly, more often than usual, or during the night. you have pain or a burning sensation when peeing. your pee looks cloudy.
Foul-smelling urine may be due to bacteria. Sweet-smelling urine may be a sign of uncontrolled diabetes or a rare disease of metabolism. Liver disease and certain metabolic disorders may cause musty-smelling urine.
A person with kidney failure may have breath that smells like ammonia or urine. Serious liver disease can make breath smell musty or like garlic and rotten eggs. Compounds that are transported through the blood can also be released through your sweat glands. That can make your armpits and skin smell bad.
Sinuses become infected when small particles such as dust, pollen, or animal dander enter the nasal passages and become trapped. This can cause inflammation, which leads to a buildup of mucus and bacteria in the sinuses. As the bacteria and mucus accumulate, they produce a foul odor that can smell like rotten eggs.
Therefore, perhaps a lack of vitamin D leads to neurological decline of the central and peripheral nervous system, including the cranial nerves, leading to reduced olfaction. The issue of reduced olfaction with vitamin D deficiency is not just an issue of mechanistic interest.
Vitamin B supplements may also contribute to strong smelling urine, which may smell slightly musty. However, this is not a cause for concern. When you don't drink enough water, urine becomes more concentrated – this is reflected in its colour and smell.
Liver disease can make urine smell musty, sweet, or like ammonia due to the buildup of toxins (like dimethyl disulfide/methyl mercaptan) that the failing liver can't process, leading to a specific scent known as foetor hepaticus, often accompanied by dark urine and jaundice. This ammonia-like odor comes from excess urea breakdown, while a sweet smell can also signal uncontrolled diabetes, so a medical evaluation is crucial.
Dietary fiber: Sulfur is one of the biggest sources of smelly farts, and many high-fiber foods contain more sulfur than other types of food. So even if a person was producing a similar amount of gas, a high-fiber diet may make that gas relatively more smelly.
Bladder infection. Cystitis (irritation of the bladder) Dehydration — when the body doesn't have enough water and other fluids to work as it should. Diabetic ketoacidosis (in which the body has high levels of blood acids called ketones)
The 5 key warning signs of a bladder infection (Urinary Tract Infection or UTI) are: pain/burning during urination, frequent/urgent need to pee (even with little output), cloudy/bloody/strong-smelling urine, lower belly/pelvic pressure, and feeling like your bladder isn't empty, with fever or back pain signaling a more serious kidney infection, requiring immediate medical attention.
Smelly urine treatment depends on the underlying cause. Options may include: Antibiotics for bacterial infections like UTIs. Antifungal medications for yeast infections.
If your kidneys aren't working properly, you may notice one or more of the following signs:
Patients affected by trimethylaminuria will often have fishy-smelling urine. Trimethylaminuria is a genetic disorder in which affected individuals have an enzymatic deficiency that makes them unable to metabolize TMA. Because they cannot metabolize TMA, affected individuals have a buildup of TMA in their bodies.
Stay Hydrated
Water helps flush out toxins and waste products from your body, allowing your kidneys to function more efficiently. Aim to drink at least 8-10 glasses of water daily, and consider increasing your intake if you're active or live in a hot climate.
Phantosmia refers to detecting smells that aren't really there. It's a symptom of many common conditions, including allergies, colds and upper respiratory infections. It could also indicate a brain-related condition, including epilepsy, stroke or Alzheimer's disease.
Urine is mostly waste products and water and normally has a mild smell and a light yellow color. If you have more waste than water in your urine, it can smell more strongly. In most cases, a strong smell isn't a sign of disease. It's usually from your diet and medications, or it means you need to drink more water.
If the enzyme is missing or its activity is reduced because of a variant in the FMO3 gene, trimethylamine is not processed properly and can build up in the body. As excess trimethylamine is released in a person's sweat, urine, and breath, it causes the odor characteristic of trimethylaminuria.