Causes of smelly urine

Overview

Smelly urine is urine that has an unusual or strong odor. In many cases, it is harmless and temporary, but it can sometimes be a sign of an underlying health condition, such as a urinary tract infection (UTI) or dehydration.

Yes, smelly urine is very common. Most people will experience it at some point in their lives, often due to harmless causes like diet or not drinking enough water.

Smelly urine can affect anyone, but it is more common in women and girls due to their shorter urethra, which makes UTIs more likely. Older adults, people with diabetes, and those who use urinary catheters are also at higher risk.

Symptoms

Common symptoms

• Urine that smells stronger than usual, often described as ammonia-like, fishy, or sulfur-like
• Changes in urine color (darker or cloudy)
• Pain or burning sensation when urinating
• Frequent urge to urinate or passing only small amounts
• Feeling that the bladder is not empty after urinating

Symptoms in children

• Children may not be able to describe the smell, so look for signs like crying or holding themselves when urinating
• Fever or fussiness without an obvious cause
• Loss of appetite or vomiting
• Strong-smelling diaper or potty urine that doesn't go away with better hydration

Symptoms in older adults

• Confusion or sudden changes in mental state (delirium) – this can be a sign of a UTI in older adults
• Incontinence (leaking urine) that is new or worse
• Fever, chills, or feeling generally unwell
• Foul-smelling urine that may be accompanied by blood or sediment

Causes

Main causes

• Dehydration – when you don't drink enough water, urine becomes more concentrated and can smell like ammonia
• Certain foods and drinks – asparagus (produces a sulfur-like smell), coffee, garlic, onions, fish, and some spices
• Urinary tract infection (UTI) – bacteria in the urine can cause a strong, fishy, or foul odor
• Kidney stones – stones can cause urine to become concentrated or infected, leading to a strong smell
• Diabetes – uncontrolled diabetes can cause sweet or fruity-smelling urine due to ketones
• Liver disease – advanced liver problems can lead to a musty or ammonia-like smell
• Metabolic conditions – rare inherited disorders can cause unusual urine odors (e.g., maple syrup urine disease)

Risk factors

• Being female (higher risk of UTIs)
• Sexual activity (increases UTI risk in women)
• Using a urinary catheter or having urinary tract abnormalities
• Diabetes, especially if blood sugar levels are not well controlled
• Older age (weakened immune system and more chronic conditions)
• Taking certain medications or supplements (but these are not named here – ask your doctor or pharmacist)

When to see a doctor

See a doctor urgently if:

• You have severe pain in your side or back
• You have a high fever with chills
• You are unable to pass urine
• You see blood in your urine
• You have confusion or are feeling very unwell

Book a routine appointment if:

• You have a bad smell that lasts more than a couple of days
• You have pain, burning, or discomfort when urinating
• You often feel the need to urinate or are going more often than usual
• Your urine looks cloudy, dark, or has sediment
• You have other symptoms like fever, nausea, or back pain that are not severe

Diagnosis

A doctor will ask about your symptoms, medical history, diet, and any medications you take. They will check for signs of infection or other conditions. A simple urine test (urinalysis) is usually the first step.

Tests that may be done

• Urine dipstick test – a plastic strip with chemicals that reacts to substances in the urine, such as signs of infection (nitrites, white blood cells) or ketones
• Urine culture – a sample of urine is sent to a lab to see if bacteria grow; this confirms a UTI and identifies the bacteria
• Blood tests – to check for diabetes, kidney or liver problems, or signs of infection
• Imaging tests (ultrasound or CT scan) – if kidney stones or other structural issues are suspected

What to expect at your appointment

The doctor will likely ask for a 'clean catch' urine sample (midstream urine) in a sterile container to avoid contamination. The test is quick and painless. Results for a dipstick may be available within minutes; a culture may take 1–2 days. You will be told the findings and advised on next steps.

Treatment

Treatment depends on the underlying cause. Most cases of smelly urine due to dehydration or diet resolve on their own with simple self-care. If an infection or other condition is found, specific treatment will be recommended by your doctor.

Self-care at home

• Drink more water throughout the day to keep urine light yellow or clear
• Avoid foods and drinks that are known to cause strong urine odor, such as asparagus, coffee, and spicy foods
• Urinate as soon as you feel the need, and empty your bladder fully each time
• Practice good hygiene: wipe front to back after using the toilet, and urinate after sexual activity
• Consider a course of probiotics or cranberry products only if recommended by your doctor (evidence is mixed)

Medical treatments

If the cause is a urinary tract infection (UTI), your doctor may prescribe a course of antibiotics – it is important to finish the full course even if you feel better. For conditions like diabetes or kidney stones, treatment focuses on managing those underlying problems. Your doctor will discuss the most appropriate treatment for your specific situation. Never share or reuse antibiotics.

When is surgery considered?

Surgery is rarely needed for smelly urine itself, but may be required if the cause is something like large kidney stones, structural problems in the urinary tract, or tumours. Your doctor will refer you to a specialist if surgery is a possibility.

Living with this condition

If you have a condition that causes recurring smelly urine (like chronic UTIs), you may need to be extra careful with hydration and hygiene. Keep a diary of when the smell occurs and any triggers. Let your doctor know if you notice changes.

Lifestyle tips

• Drink plenty of fluids (aim for 6–8 glasses of water a day unless your doctor has advised otherwise)
• Don't hold your urine – go when you feel the urge
• Wear cotton underwear and avoid tight-fitting trousers
• Take showers instead of baths to reduce the risk of irritation

Diet and exercise

A balanced diet and regular exercise can help keep your immune system strong and may reduce the risk of UTIs. If you have diabetes, controlling your blood sugar through diet and activity is especially important to prevent smelly urine caused by ketones.

Mental health and emotional wellbeing

Having smelly urine can be embarrassing or anxiety-provoking, especially if it happens often. Remember that it is usually harmless and treatable. If you feel upset or stressed, talk to a trusted friend or healthcare professional. You are not alone.

Prevention

Not all causes can be prevented, but many cases of smelly urine can be avoided by staying well hydrated, practising good hygiene, and managing chronic conditions like diabetes. Avoiding foods that trigger bad smells can also help.

Vaccines

There are no vaccines specifically for smelly urine. However, the flu vaccine and pneumococcal vaccine are recommended for older adults and people with long-term health conditions to prevent infections that could lead to UTIs.

Screening programmes

There is no routine screening for smelly urine. If you have diabetes, regular urine tests are often part of your check-ups. If you have recurrent UTIs, your doctor may suggest regular monitoring.

Complications

If left untreated

• If a UTI is not treated, the infection can spread to the kidneys (pyelonephritis), causing more serious illness
• Severe kidney infections can lead to permanent kidney damage or sepsis (a life-threatening response to infection)
• Untreated diabetes (causing sweet-smelling urine) can lead to diabetic ketoacidosis (DKA), a medical emergency

Long-term outlook

The outlook for smelly urine is excellent. Most cases are harmless and resolve on their own with simple measures. Even when an infection or underlying condition is the cause, early treatment is highly effective and complications are rare. With proper care, you can manage the symptoms and stay healthy.

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