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Trimethylaminuria - Causes, Symptoms, Diagnosis, and Treatment

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Trimethylaminuria is a rare disorder that causes a fishy smell due to the body’s inability to break down trimethylamine. Read more about this condition.

Medically reviewed by

Dr. Penchilaprasad Kandikattu

Published At June 15, 2023
Reviewed AtJune 15, 2023


Trimethylamine has a powerful smell, similar to that of rotten fish. In individuals with trimethylaminuria, the chemical trimethylamine collects up in the body, causing it to release a solid fishlike odor. However, it can also be described as smelling like other things.

Trimethylaminuria has no associated health complications, but the pungent odor may affect people psychologically and socially.

The article below describes the causes, symptoms, and management of trimethylaminuria.

What Is Trimethylaminuria?

Trimethylaminuria is a rare disorder causing a person to have an excess buildup of the chemical trimethylamine in the body.

Other names to refer to trimethylaminuria are:

  • Fish odor syndrome.

  • Stale fish syndrome.

  • Fish malodor syndrome.

  • TMAuria.

  • TMAU.

Trimethylamine is found in foods that contain carnitine, choline, and trimethylamine N-oxide, known as TMAO. Examples of these foods are eggs and liver.

Usually, trimethylamine gets broken down by an enzyme as part of the digestion process.

In some people, the gene that controls this enzyme undergoes mutation (alteration), preventing it from adequately breaking down certain chemicals. This results in trimethylamine building up in the body. Trimethylamine has a fishlike solid odor. This is because when people can not break down trimethylamine, the chemical gets released by the body through bodily fluids.

What Are the Symptoms of Trimethylaminuria?

The primary symptom of trimethylaminuria is a fishlike solid odor. Excess trimethylaminuria is released by the body through:

  • Sweat.

  • Breath.

  • Urine.

  • Reproductive fluids.

The intensity of the odor changes from a mild odor to a persistent strong odor. Certain factors, such as excess sweating, may elevate the smell. In addition, it has been observed that the odor worsens with exercise or stress.

Trimethylaminuria is found to be more common in females than in males. Although the reason for this is unclear, researchers imply that female sex hormones, such as estrogen and progesterone, could have a role to play.

Females may have more severe symptoms:

  • Just before the onset of menstruation.

  • During menstruation.

  • After oral contraceptives.

  • Around menopause.

Diet and stress levels may also act as trigger factors.

Other than a fishlike odor, no other symptoms are seen in people with trimethylaminuria. Also, the disorder does not lead to any other health issues. However, the pungent smell might affect the emotional, mental, or social health of individuals with this disorder. These individuals may isolate themselves from social gatherings or experience depression and anxiety due to the condition.

What Causes Trimethylaminuria?

Trimethylaminuria is a genetic condition that occurs due to a mutation in the flavin-containing monooxygenase 3 (FMO3) gene. An alteration in the FMO3 gene affects the FMO3 enzyme. This enzyme helps convert trimethylamine to trimethylamine N-oxide, which has no odor. Trimethylaminuria is an autosomal recessive disease, meaning for a person to develop this condition, they must acquire two mutated FMO3 genes, one from each parent. If they receive just one affected gene, they will be a carrier. If the FMO3 enzyme does not work correctly, the body cannot break down trimethylamine, leading to the build-up of the chemical in the body. The body then releases this strong-smelling chemical through bodily fluids, such as sweat and urine.

The symptoms of trimethylaminuria vary significantly among individuals. In addition, researchers suggest that various types of mutations in the FMO3 gene can affect the intensity of the symptoms.

People may sometimes develop secondary trimethylaminuria from large doses of trimethylamine or products that trigger trimethylamine production.

These include:

  • L-carnitine - Supplement that is famous among athletes.

  • Choline - An ingredient used to treat Huntington’s and Alzheimer’s diseases.

  • Lecithin - An additive that is added to a range of health supplements.

Symptoms appear when the FMO3 enzyme in the liver cannot break down excess triethylamine.

How Is Trimethylaminuria Diagnosed?

The healthcare provider may be able to diagnose trimethylaminuria by asking about the symptoms and ordering a few tests. For example, a urine test can indicate whether a person has increased levels of trimethylamine in their urine. A genetic test may also help diagnose the condition by showing whether the FMO3 gene underwent mutation, causing trimethylaminuria.

What Is the Treatment of Trimethylaminuria?

Currently, there is no cure available for trimethylamine, so treatment focuses on the management and reduction of symptoms.

People can reduce the strong smell of trimethylamine by avoiding certain substances that can increase the production or levels of trimethylamine in the body, such as lecithin and choline.

The milk produced by wheat-fed cows contains trimethylamine, while foods containing choline


  • Beans.

  • Eggs.

  • Peanuts.

  • Liver.

  • Kidney.

  • Peas.

  • Soy products.

  • Brassica vegetables, like cabbage, broccoli, cauliflower, and brussels sprouts.

  • Fish oil supplements containing lecithin.

Trimethylamine N-oxide is found in seafood, cephalopods (octopus and squids), and crustaceans (such as crabs and lobsters). It is also present at lower levels in freshwater fish.

Other ways to reduce symptoms include:

  • Taking a small dose of antibiotics can decrease the bacteria in the gut and prevent trimethylamine production.

  • Taking a laxative to reduce the time the food takes to pass through the digestive tract can help lower the amount of trimethylamine produced by the gut.

  • If possible, avoid activities that can cause excess sweating, such as intense exercise or emotional stress.

Certain supplements may help to reduce trimethylamine in a person’s urine. Below are the recommendations from the National Human Genome Research Institute:

  • 750 milligrams (mg) of activated charcoal twice daily for ten days.

  • 60 milligrams copper chlorophyllin three times a day after meals for three weeks.

Vitamin B2 or riboflavin may help to increase the activity of the existing FMO3 enzyme in the body. The recommended dosage is 30 to 40 milligrams between three and five times daily with meals.

People with trimethylaminuria can also avoid using alkaline soaps and applying body lotions with a high pH level. Instead, applying slightly acidic soaps or low pH (5.5 to 6.5) body lotions can help to easily wash off trimethylamine from the skin.

If trimethylaminuria causes a psychological or social impact, a doctor or counselor should be consulted. Counseling with a family member may also be helpful.


Trimethylaminuria is a rare condition that leads to a buildup of trimethylamine in the body, emitting a strong fishy odor. Most individuals with trimethylaminuria can successfully reduce the odor with dietary and lifestyle changes. However, people must seek help from a healthcare professional if trimethylaminuria leads to social isolation, anxiety, depression, or other psychological issues.

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Dr. Penchilaprasad Kandikattu
Dr. Penchilaprasad Kandikattu

Internal Medicine


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