A person’s urine might smell like fish for a variety of reasons, such as diet, infections, or taking certain supplements. Some chronic conditions may also alter the smell of urine.

If fishy-smelling urine is a person’s only symptom, they may want to wait for a couple of days to see if it clears up. Drinking more water may help.

However, if a person has a fever, pain, or difficulty urinating, they should speak with a doctor right away.

In this article, we look at the causes, symptoms, and treatments for urine that smells like fish.

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Urine that smells fishy is not common. Urine is 75% water, and so when a person is healthy and well-hydrated, it should not have a noticeable unpleasant odor.

When urine does have a fishy smell, the culprit may be a chemical known as trimethylamine (TMA). This is the compound that gives fish a bad smell when it decomposes, as bacteria begin to grow.

TMA can also occur naturally in the body due to certain bacteria.

Some causes of fishy-smelling urine are mild or temporary, such as:

  • Vitamins and supplements: Some vitamin supplements, such as vitamin B6, can affect the way urine smells. This may be especially noticeable if a person has not had enough water to drink.
  • Diet: Certain foods, such as asparagus, can give urine a strong smell. If foods are responsible, avoiding them should mean the odor goes away.
  • Medications: Some medications may change the way urine smells. If a person suspects this could be the case, they should speak with their doctor. Do not stop or change the dosage without consulting a medical professional.

Fishy-smelling urine can be a symptom of a health condition that requires treatments. Sometimes, it may be the only symptom, or an early symptom. In other cases, a person may have several symptoms.

In either case, a person should contact a doctor if they cannot identify the cause of a fishy odor, or the cause could be one of the following.

Urinary tract infections (UTIs)

A UTI occurs when harmful bacteria grow in the urinary tract. This can make the urine smell.

Other symptoms may include:

  • frequently needing to urinate
  • pain when urinating
  • urinary urgency
  • cloudy urine
  • blood in the urine
  • fever or chills

Doctors can treat UTIs with antibiotics. Anyone who suspects that they have a UTI should speak with a doctor, particularly if they are pregnant.

Bacterial vaginosis (BV)

This bacterial infection causes a fishy-smelling discharge to come from the vagina. The discharge may be watery and grey, or yellow-green in color.

While BV does not directly affect urine, a person may notice the smell when they use the bathroom, or the discharge may mix with urine when a person urinates.

The smell and other symptoms may get worse immediately after sex or when menstruating. BV is treatable with topical or oral antibiotics.

Fish odor syndrome

Trimethylaminuria, also known as fish odor syndrome, is a rare disorder that causes a person’s bodily fluids to smell like fish. This can include the urine.

A person develops this condition when they are not able to break down TMA. A person may have the symptoms all the time, or they may come and go. Factors that may exacerbate the symptoms include:

  • stress
  • periods
  • eating certain foods, such as fish, beans, or eggs
  • sweating

In many cases, the disorder is genetic and causes no other symptoms. However, people can acquire the condition, too. This may occur if a person takes large doses of choline or l-carnitine, or if they have an imbalance of gut bacteria.

The symptoms of trimethylaminuria may be present from birth, but they can develop later on. Often, this occurs around puberty.

If a person notices a fishy smell in their urine, saliva, or sweat despite maintaining good personal hygiene, they should speak with a doctor.

Kidney infections

UTIs can spread to the kidneys, causing many of the same symptoms, such as unpleasant-smelling urine.

The symptoms of a kidney infection may include:

  • difficulty urinating, or painful urination
  • pain in the lower back
  • a high fever
  • blood in the urine
  • general malaise

Kidney infections can become serious. Some may require hospitalization, though some are treatable at home with antibiotics. Anyone with symptoms of a kidney infection should see a doctor right away.

Prostatitis

Prostatitis describes swelling and inflammation of the prostate gland, which is located below the bladder in males.

The inflammation can be the result of an infection, in which case, a person may notice an unpleasant smell when they urinate.

The symptoms of prostatitis are similar to those of a UTI. Additional signs may include:

  • 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

Similarly to the kidneys, the liver helps the body to filter out certain chemicals. When the liver is not functioning correctly, more of these chemicals enter the urine, which may affect how it smells.

Other symptoms of liver failure include:

  • unexplained nausea or vomiting
  • loss of appetite
  • yellow skin, nails, or eyes (jaundice)
  • 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 have potential symptoms of liver failure:

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

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

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

People who also have pain, a fever, or signs of kidney or liver problems should call a doctor or visit the emergency room immediately.

Urine that smells fishy is not typical, but many of the causes are mild or treatable. Certain supplements, medications, or foods may change how urine smells. Some infections, such as UTIs or BV, can also cause this symptom.

Occasionally, a more serious or long-term condition may be responsible, which may require urgent treatment or ongoing management. A doctor can provide a diagnosis and recommend the best treatments.