What causes smelly urine?

Urine often has a slight ammonia smell, especially first thing in the morning or when a person is dehydrated.

Smelly urine can also be a sign of an infection, however, so if the smell does not go away on its own, or if additional symptoms develop, see a doctor.

In this article, we explore what causes smelly urine and offer strategies to reduce the smell.

Common issues that cause smelly urine

SDehydration and some medications may cause smelly urine.

Smelly urine does not always stem from a health condition. Dehydration, some vitamins, and some medications can give urine an unpleasant odor.

Common causes of smelly urine include:

Concentrated urine

When urine is highly concentrated, it contains more ammonia and less water. This can cause it to have a strong smell.

Urine tends to be more concentrated when a person is dehydrated. This is often the case first thing in the morning or when a person does not drink enough water throughout the day.

Symptoms of severe dehydration include:

• dry mouth
• lethargy
• muscle weakness
• headaches
• dizziness

If any symptom of dehydration does not go away after the person has drunk plenty of water, they should see a doctor. The underlying issue may be a kidney infection.

Foods

Metabolites are any substances that form during digestion. As the body excretes them in urine, some can cause the urine to smell.

When asparagus, for example, is broken down during digestion, its metabolites give urine a foul smell.

Medication and supplements

Some medications and supplements that can lead to a change in the odor of urine include:

• high doses of the B vitamins thiamin and choline
• some antibiotics, especially a group called sulfonamides
• some diabetes medications
• chemotherapy

Medical conditions

Some health issues that lead to smelly urine require short courses of treatment, while others require more lasting attention.

Urinary tract infection

A urinary tract infection (UTI) happens when harmful bacteria proliferate in the urethra, bladder, or kidneys.

Most people have symptoms beyond smelly urine, including:

• pain when urinating
• a frequent, intense need to urinate
• difficulty fully emptying the bladder
• cloudy or dark urine
• blood in the urine
• a fever, if the infection has spread
• back pain, if the infection has spread to the kidneys

Infections with certain bacteria, notably Aerococcus urinae, may cause very bad-smelling urine, with or without other symptoms.

A UTI usually clears up with antibiotics. If a person does not receive treatment, the infection can spread, so see a doctor as soon as possible.

Bacterial vaginosis

The vaginal infection bacterial vaginosis causes a distinct fishy odor that may be worse after sex. Other symptoms include:

• pain
• itching
• burning pain while urinating
• thin, white or gray discharge

Diabetes

Diabetes medications may change the smell of urine, and so too can the disease — especially if blood sugar levels go uncontrolled.

Some people notice a very sweet smell. This happens when there is too much sugar in the urine.

Other symptoms of diabetes include:

• going to the bathroom frequently, especially at night
• intense thirst
• fatigue
• weight loss, in some cases
• genital itchiness
• slow wound healing
• blurred vision
• high blood pressure

Organ failure

When organs involved in digestion or urination are not working properly, it can affect the way urine smells.

According to one 2012 study, some people with kidney failure, for example, notice a bad body odor or foul-smelling urine. Another 2012 study found that liver disease can change the way urine smells.

The symptoms of organ failure vary, depending on the area involved and the cause. Liver failure also tends to cause yellowing of the skin or eyes, while kidney failure may also cause pain during urination.

Can asparagus make urine smell? 

Some people find that asparagus gives their urine a strong, foul odor that may last from a few hours to a few days.

Some people may not be able to detect the odor. Research from 2016 suggests that about 60% of people have one of several genetic variants that either decreases their ability to smell asparagus in urine or eliminates it entirely.

Can pregnancy cause smelly urine? 

Some people notice a change in the smell of their urine during pregnancy. Various hormonal changes involved may change the smell of urine — or the person’s sensitivity to smells.

Many people report a stronger sense of smell during pregnancy, though very little research has looked into this phenomenon.

It is worth noting that pregnant people with UTIs may not have any more noticeable symptoms — a change in the odor of urine may be the only warning.

Prompt treatment of UTIs decreases the risk of serious complications for both the person and their baby.

Strategies for reducing the smell

The following tips may help:

• Avoid eating foods that cause urine to smell, especially asparagus.
• Switch supplements, if high levels of thiamin or choline are likely to be the culprit.
• Drink plenty of water to support hydration and kidney and urinary tract health.
• Visit the bathroom as soon as the urge strikes.
• Manage any chronic medical conditions, such as diabetes, as carefully as possible, with the guidance of a doctor.

Also, having an overall healthy lifestyle and reducing or eliminating alcohol intake can protect the liver and may help get rid of the smell.

Diagnosing the cause of smelly urine

The doctor will ask about certain lifestyle factors, recent health changes, and when the bad smell began. They may do a urine culture to check for bacteria and other signs of infection.

When the diet is responsible for the smell, the doctor may be able to diagnose the problem based on symptoms alone.

In some cases, the doctor may order imaging scans of the urinary tract or kidneys. A person may also need blood work to check for other health conditions.

When to see a doctor

A bad smell in the urine often goes away on its own, especially when dehydration or something in the diet causes it.

A person does not need to see a doctor if they can identify a harmless cause of their smelly urine, such as asparagus.

Other causes need medical treatment. While a UTI is relatively harmless, it can progress and cause serious health issues, including kidney infections. With early treatment, a person should feel better in a few days.

Because some people with UTIs have no symptoms, see a doctor if the bad smell lasts longer than a few days. This is especially important for people who are pregnant.

Other health issues that can cause this odor require ongoing treatment. For example, a person with diabetes may need to switch medications or make certain lifestyle changes.

If a person who has any chronic condition finds that the smell of their urine changes significantly, it may be a good idea to flag it with a doctor.

Summary 

Foul-smelling urine can be alarming, but it may be short-lived, and drinking more water may help the smell fade faster.

However, if there is not a clear cause — such as asparagus, supplements, or dehydration — it is a good idea to consult a healthcare provider.