Why does my urine smell like fish?

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A fishy smell is uncommon in urine. Many of the causes are not serious, but it can sometimes indicate a severe condition, such as damage to the kidneys or liver.

In many cases, the culprit responsible for the smell of fish is a chemical called trimethylamine oxide. When a fish dies and bacteria begin to decompose the tissue, this chemical is released and converted to trimethylamine (TMA), which causes the fishy odor.

A fishy smell in urine may be caused by the presence of bacteria, TMA, or an interaction between them.

According to a study from 2013, most healthy people produce chemicals that break down TMA, which stops them from smelling like fish, even when they have eaten fish recently or have a lot of bacteria in their systems.

If a person suspects that any of the following causes are responsible for the fishy smell, it is usually safe to wait a few days and see if the smell clears up without treatment.

Pregnancy

Pregnancy can make the urine more concentrated. This can lead to a stronger smell, and it may make a fishy smell more noticeable. See a doctor if the smell does not disappear in a day or two.

Dehydration during pregnancy can make the urine look darker or smell worse. A person who is pregnant and noticing these symptoms should ensure that they are drinking enough water.

Vitamins and supplements

Some of these can make the urine smell fishy, especially supplements of calcium, vitamin B6, and vitamin D. The odor may be more noticeable when a person is dehydrated. If an individual stops taking these supplements and their urine still smells fishy, they should contact a doctor.

Diet

Certain foods, including asparagus and fish, can make the urine smell. If foods are responsible, the smell should go away after a few hours.

Fishy-smelling urine may be the first indication of a mild or severe health problem. Some people may have no other symptoms or several. In either case, a person should contact a doctor if they cannot identify the cause of a fishy odor.

The following causes often require medical attention:

Urinary tract infections (UTIs)

A UTI occurs when too much harmful bacteria grow in the urinary tract. This can make the urine smell. In some people, a UTI causes no symptoms. When symptoms are present, they often include:

• pain when urinating
• an intense need to urinate
• frequently needing to urinate, even immediately after using the bathroom
• blood in the urine

Most UTIs can be treated with antibiotics. If left untreated, a UTI may spread to the kidneys.

Anyone who suspects that they have a UTI should see a doctor.

Bacterial vaginosis (BV)

This bacterial infection in the vagina causes fishy, foul-smelling discharge. While it does not affect the urine, a person may notice the odor while using the bathroom.

The smell and other symptoms may get worse immediately after sex. Women with BV may believe that they have a yeast infection, but the smell is a distinguishing factor. Some other symptoms include:

• burning in or around the vagina
• pain during sexual intercourse
• gray or frothy vaginal discharge

BV is common in sexually active women. Some sexually transmitted infections may also cause an unusual odor, and it is important to see a doctor for testing.

Fish odor syndrome

Trimethylaminuria, better known as fish odor syndrome, is a rare disorder that causes a person’s bodily emissions to smell like fish. The odor can arise from the saliva, sweat, or urine. A person develops this condition when they are not able to break down TMA.

In many cases, the disorder is passed genetically and causes no other symptoms. Less often, a person who has a diet very high in TMA and unusual bacteria in the gut can develop the syndrome.

A person emitting a fishy odor that persists, in spite of good hygiene, should see a doctor. Dietary changes, antibiotics, and nutritional supplements may help.

Kidney problems

The kidneys filter the urine, which helps to remove toxins from the body. When the urine smells, it may indicate that the kidneys are not functioning correctly, often due to infections or kidney stones.

Symptoms of a kidney infection may include:

• difficulty urinating, or painful urination
• a UTI that gets worse
• pain in the lower back
• a high fever
• blood in the urine

Kidney infections may require hospitalization, though some can be managed at home with antibiotics. Anyone with symptoms of a kidney infection should see a doctor right away.

Kidney stones are mineral deposits that collect in the kidneys. They can be as small as a grain of rice or grow to resemble pebbles and small rocks.

Passing a kidney stone can be painful. Sometimes they become stuck. A person who is first experiencing symptoms, or who notices bleeding when trying to pass a kidney stone, should see a doctor. Drinking plenty of water can help the stone to pass more quickly.

Prostatitis

Prostatitis describes swelling and inflammation of the prostate, and it is often the result of an infection. People with prostatitis may notice changes in urination, including a fishy smell.

Symptoms of prostatitis are similar to those of a UTI. People with prostatitis may also experience:

• pain in the anus, perineum, or scrotum
• lower back pain
• chills and body aches
• a weak urine stream

Treatment depends on the cause of the inflammation. A doctor may prescribe medication, such as antibiotics and pain relievers, or they may recommend surgery. Warm sitz baths can help with managing the pain at home.

Liver failure

Like the kidneys, the liver helps the body to filter out toxins. When the liver is not functioning correctly, it releases more of a substance called bilirubin into the blood. This can pass into the urine, making it smell bad.

Symptoms of liver failure include:

• unexplained nausea or vomiting
• loss of appetite
• yellow skin, nails, or eyes
• itching
• retaining fluid
• swollen ankles
• exhaustion
• diarrhea

Some people are more susceptible to liver failure than others. Anyone with one or more of the following conditions should contact a doctor immediately if they suspect that their liver is failing:

• hepatitis
• fatty liver disease
• any autoimmune disease
• cirrhosis
• bile duct disease
• metabolic disorders

Treatment will depend on the extent of the liver failure, but it may include medication, hospitalization, or a liver transplant.

Fishy-smelling urine is not often a medical emergency. However, people who experience pain, a fever, or signs of kidney or liver problems should call a doctor or visit the emergency room.

When no other symptoms are present, the smell may disappear without treatment in a few days. If this does not happen, a person should consult a doctor.

It is easy to overlook urine as an indicator of health, but it can provide important information about how well the body is functioning.

While fishy-smelling urine may be alarming, the causes are usually minor. A doctor can provide a diagnosis and recommend the quickest path to recovery.

A fishy smell in the urine will often go away without treatment in a few days. If the smell does not improve, seek medical attention. Serious conditions can occasionally be responsible for this odor, and prompt treatment can be vital.