Trimethylaminuria ( fish odour syndrome )

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.

Trimethylaminuria (Fish Odor Syndrome)

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.

Overview

Trimethylaminuria makes people smell like rotten fish. Avoiding the foods pictured above may help reduce trimethylaminuria symptoms.

What is trimethylaminuria (TMAU)?

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.

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.

Types of TMAU

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.

How common is this condition?

One study suggests between 1 in 200,000 and 1 in 1 million people worldwide have trimethylaminuria. TMAU typically affects people assigned female at birth (AFAB) more than it does people assigned male at birth (AMAB).

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.

Symptoms and Causes

What are the symptoms of trimethylaminuria?

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.

What causes TMAU?

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.

What are complications of this condition?

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.

Diagnosis and Tests

How is trimethylaminuria diagnosed?

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.

Management and Treatment

What are treatments for 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.

What foods should I avoid?

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.

What medication is used for trimethylaminuria?

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.

Trimethylaminuria (‘fish odour syndrome’)

Sometimes it’s caused by faulty genes that a person inherits from their parents, but this isn’t always the case.

There’s currently no cure, but there are things that can help.

Symptoms of trimethylaminuria

Trimethylaminuria symptoms can be present from birth, but they may not start until later in life, often around puberty.

The only symptom is an unpleasant smell, typically of rotting fish – although it can be described as smelling like other things – that can affect the:

The smell may be constant or may come and go. Things that can make it worse include:

• sweating
• stress
• certain foods – such as fish, eggs and beans
• periods

When to see a GP

See a GP if you notice a strong, unpleasant smell that doesn’t go away.

Tell your GP if you think it might be trimethylaminuria. It’s an uncommon condition and they may not have heard of it.

They may refer you to a specialist for tests to check for the condition.

Causes of trimethylaminuria

In trimethylaminuria, the body is unable to turn a strong-smelling chemical called trimethylamine – produced in the gut when bacteria break down certain foods – into a different chemical that doesn’t smell.

This means trimethylamine builds up in the body and gets into bodily fluids like sweat.

In some cases, this is caused by a faulty gene a person has inherited from their parents.

How trimethylaminuria is inherited

Many people with trimethylaminuria inherit a faulty version of a gene called FMO3 from both their parents. This means they have 2 copies of the faulty gene.

The parents themselves might only have 1 copy of the faulty gene. This is known as being a “carrier”. They usually won’t have symptoms, although some may have mild or temporary ones.

If you have trimethylaminuria, any children you have will be carriers of the faulty gene so are unlikely to have problems. There’s only a risk they could be born with the condition if your partner is a carrier.

Genetic counselling may help you understand the risks of passing trimethylaminuria on to any children you have.

Treatments for trimethylaminuria

There’s currently no cure for trimethylaminuria, but some things might help with the smell.

Foods to avoid

It can help to avoid certain foods that make the smell worse, such as:

• cows’ milk
• seafood and shellfish – freshwater fish is fine
• eggs
• beans
• peanuts
• liver and kidney
• supplements containing lecithin

It’s not a good idea to make any big changes to your diet on your own, particularly if you’re pregnant or planning a pregnancy, or are breastfeeding.

Your specialist can refer you to a dietitian for advice. They’ll help you make sure your diet still contains all the nutrients you need.

Other things you can do

It can also be helpful to:

• avoid strenuous exercise – try gentle exercises that don’t make you sweat as much
• try to find ways to relax – stress can make your symptoms worse
• wash your skin with slightly acidic soap or shampoo – look for products with a pH of 5.5 to 6.5
• use anti-perspirant
• wash your clothes frequently

Treatments from a doctor

Your doctor may recommend:

• short courses of antibiotics – this can help reduce the amount of trimethylamine produced in your gut
• taking certain supplements – such as charcoal or riboflavin (vitamin B2)

Support

Many people find living with trimethylaminuria difficult. Feelings of isolation, embarrassment and depression are common.

Tell your doctor if you’re struggling to cope. They may recommend seeing a counsellor for emotional support.

Page last reviewed: 16 April 2021
Next review due: 16 April 2024

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