Trimethylaminuria (Fish Odor Syndrome or TMAU)

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Trimethylaminuria (TMAU, fish odor syndrome) is an uncommon condition that makes people smell like rotten fish. It’s a metabolic disorder. People with TMAU may develop depression and anxiety. There’s no cure for TMAU. But healthcare providers may recommend that you change food choices, stress management techniques and medication to reduce symptoms.

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Trimethylaminuria (trī-meth'il-am-i-nyūr'ē-ă) is a metabolic disorder that makes your sweat, breath, saliva and pee smell like rotten fish. Metabolic disorders affect how your body processes nutrients and enzymes. Healthcare providers may refer to this condition as TMAU or fish odor syndrome.

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There’s no cure for TMAU. But changing the kinds of food that you eat, using certain soaps and lotions, and managing stress can help reduce trimethylaminuria symptoms.

Trimethylaminuria may be primary or secondary:

Primary trimethylaminuria: People with primary TMAU inherit certain genetic mutations (changes) from their biological parents.
Secondary trimethylaminuria: Some medical conditions and dietary supplements may lead to fish odor syndrome.

One study suggests between 1 in 200,000 and 1 in 1 million people worldwide have trimethylaminuria. TMAU typically affects females more than it does males.

Some researchers believe it may be more common than the data shows. Research shows that often, people believe their personal hygiene habits are responsible for their situation, so they don’t seek medical care or receive a diagnosis of TMAU.

People with TMAU give off an unpleasant nauseating odor that people describe as smelling like rotten fish. The odor may be body odor, bad breath (halitosis) or strong-smelling pee.

Sometimes, people only notice TMAU symptoms when the person who has the condition sweats or is experiencing stress. But some people with trimethylaminuria carry such a strong scent that others notice the scent just from being in the same room, standing across a counter or sitting in the same section of a bus or train.

Trimethylaminuria happens when something affects the FMO3 enzyme so it doesn’t work like it should. FMO3 stands for flavin-containing monooxygenase 3. This enzyme manages the impact that trimethylamine has on your body. Trimethylamine is a smelly chemical your body produces when you eat certain foods like fish, beans and eggs.

Normally, there’s a check-and-balance relationship between trimethylamine and FMO3: when your body produces trimethylamine, FMO3 enzymes break it down. That way, the chemical doesn’t smell bad when it moves from your digestive system into your bloodstream. When that doesn’t happen, trimethylamine builds up in your body, eventually seeping into your system so that your breath, sweat, saliva and pee smell like rotten fish.

People with primary trimethylaminuria develop the condition because they inherit abnormal FMO3 genes from both of their biological parents. In secondary TMAU, something keeps your FMO3 enzyme from breaking down trimethylamine. This can happen if:

You have an illness, like liver failure or viral hepatitis, that keeps the enzyme from breaking down the trimethylamine.
There’s an imbalance in your gut microbiome so there’s more trimethylamine in your system than the FMO3 enzymes can change into the non-smelly version of the chemical.
You take choline or carnitine supplements. These nutrients play a role in producing trimethylamine.

Trimethylaminuria can damage your quality of life. Research shows people with the condition often avoid relationships, jobs and activities where others may notice the unpleasant smell that TMAU causes. People with this condition may develop mental health issues, including:

Rarely, people with TMAU have suicidal behavior, where they consider suicide.

Healthcare providers diagnose TMAU by measuring the amount of trimethylamine in your urine (pee). They may order genetic tests to find out if you have primary (inherited) or secondary trimethylaminuria.

Your healthcare provider may recommend avoiding certain foods that make your body produce the chemical that causes TMAU. They may also suggest using specific soaps and lotions to help remove the fishy smell from your skin. They may prescribe medication and mental health support.

If you have trimethylaminuria, healthcare providers may recommend you avoid the following foods:

Food type Foods to avoid Proteins and certain dairy Eggs, liver, seafood and soy products and milk from wheat-fed cows. Vegetables Beans, broccoli, brussel sprouts, cabbage, cauliflower, peanuts and peas. Supplements Fish oil, choline and carnitine supplements. Food type Proteins and certain dairy Foods to avoid Eggs, liver, seafood and soy products and milk from wheat-fed cows. Vegetables Foods to avoid Beans, broccoli, brussel sprouts, cabbage, cauliflower, peanuts and peas. Supplements Foods to avoid Fish oil, choline and carnitine supplements.

Your provider may prescribe the following medications to ease TMAU symptoms:

Antibiotics and probiotics: These drugs help reduce bacteria in your gut, so your body doesn’t produce as much of the chemical that causes TMAU.
Activated charcoal: This drug binds to trimethylamine and moves it out of your system.
Antidepressants and anti-anxiety medications: These drugs treat mental health issues that some people with TMAU develop.

Your provider may recommend that you have mental health support like talking with a psychologist or counselor, particularly if you’re dealing with self-esteem and body image issues. Mental health treatment may focus on coping strategies and ways to manage your stress.

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Trimethylaminuria is a chronic condition. There isn’t a way to cure it and it doesn’t go away on its own. But there are treatments and things you can do to reduce TMAU symptoms and the condition’s impact on your life.

Self-care is an important part of living with TMAU, including:

Personal care: Using low pH soaps and lotions may reduce your body odor. Ask your healthcare provider for recommendations, including the right pH level.
Watch what you eat: Many foods make trimethylaminuria worse. Consider talking to a nutritionist about meal plans and food choices so you get enough nutrients.
Manage your stress: Stress can make TMAU symptoms worse. Ask your provider about stress management techniques that can help you lower stress that leads to a more noticeable odor.
Find support: Trimethylaminuria is an uncommon condition that can make you feel isolated. Connecting with others who have the condition may help.

Talk to your provider if changing the kinds of food that you eat or managing stress doesn’t help ease your symptoms. They’ll have other treatment options for you to consider.

Trimethylaminuria is an uncommon condition, so you may not know much about it. Here are some questions you may want to ask your healthcare provider:

Why do I have this condition?
What treatment do you recommend?
Can you recommend a support group or program?

Yes, just like typical body odor or sweat, people with TMAU may notice how they smell. But like typical body odor or sweat, some people with this condition may be accustomed to the smell and less likely to react to it than people around them. That being said, not everyone with this condition notices anything unusual.

Trimethylaminuria is an uncommon metabolic condition that makes people smell bad. It doesn’t hurt, at least in the sense that it doesn’t cause physical pain. But it can cause deep emotional wounds that are slow to heal. Some people who have trimethylaminuria go into self-imposed social exile to avoid offending others. Even after changing food choices and other steps, some people with TMAU believe they still need to keep life at arm’s length. Social isolation may make you feel depressed or anxious. If that’s your situation, ask your healthcare provider for help, including mental health support. They understand what you’ve experienced and can recommend helpful programs and services.

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Flaherty CC, Phillips IR, Janmohamed A, et. al. Living with trimethylaminuria and body and breath malodour: personal perspectives. (https://pubmed.ncbi.nlm.nih.gov/38238734/)BMC Public Health. 2024 Jan 18;24(1):222. Accessed 4/5/2024.
National Genome Research Institute (U.S.). About Trimethylaminuria (https://www.genome.gov/Genetic-Disorders/Trimethylaminuria). Updated 12/18/2018. Accessed 4/5/2024.
Phillips I, Shephard E, Primary Trimethylaminuria (https://www.ncbi.nlm.nih.gov/books/NBK1103/#_NBK1103_pubdet_). 2020 Nov 5. In: GeneReviews ®[Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Accessed 4/5/2024.

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