Health condition
Trimethylaminuria (TMAU)
Trimethylaminuria - 'fish odour syndrome' - is a genuine metabolic condition (FMO3 gene variants) in which trimethylamine from gut bacteria cannot be neutralised and escapes in sweat, breath and urine; diet and targeted measures reduce it substantially.
Why trust this guide
- 01
Editorial team
Written by our editorial team from the UK sources listed on each page.
- 02
Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
- 03
Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
-
Caused by FMO3 variants; autosomal recessive, with milder variant combinations causing intermittent symptoms - especially around menstruation
-
The odour is episodic and diet-dependent, which is partly why sufferers are often disbelieved - many have normal or heightened ability to smell it on themselves when others cannot
-
Diagnosis: urinary trimethylamine to TMA-N-oxide ratio (ideally after a choline-rich challenge), plus FMO3 sequencing
-
Management: reducing choline and TMA-precursor intake (marine fish, eggs, liver, certain legumes), short courses of gut-directed antibiotics, activated charcoal, riboflavin and pH-adjusted washing all have evidence
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
TMAU carries a psychological weight out of proportion to its biochemistry: an intermittent body odour that colleagues notice but clinicians cannot reproduce in clinic, years of scrupulous hygiene that changes nothing, and frequent misdirection toward psychiatric explanations - when the underlying fact is a liver enzyme, FMO3, failing to oxidise the fishy amine that gut bacteria make from dietary choline and carnitine. Severity tracks enzyme residual function and substrate load, which is exactly why symptoms wax with diet, hormones and stress, and why secondary forms appear with liver disease or gut dysbiosis.
Testing, surveillance and specialist care
A proper work-up - the urinary TMA ratio under standardised conditions, with FMO3 genotyping to confirm primary disease - replaces doubt with a mechanism, and structured management (dietitian-guided precursor reduction that protects nutrition, riboflavin as an FMO3 cofactor, judicious antibiotic cycles, practical washing chemistry) reduces odour meaningfully for most. Psychological support has a legitimate place after years of social injury, and carrier counselling is available for families. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a metabolic physician (inherited metabolic disease clinic). Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.
Frequently asked
Common questions about Trimethylaminuria (TMAU).
Quick, plain-English answers to what people ask us most.
-
What is trimethylaminuria (TMAU)?
It is a rare metabolic condition, sometimes called fish odour syndrome, in which the body can't properly break down a compound called trimethylamine, leading to its build-up and release in sweat, urine and breath, causing a fishy odour.
-
What causes TMAU?
It is usually caused by a deficiency in the FMO3 enzyme, which normally breaks down trimethylamine produced by gut bacteria from certain foods; this can be genetic or, less often, temporary due to liver or gut factors.
-
What are the symptoms of TMAU?
The main symptom is a persistent fishy body odour, often worsened after eating foods rich in choline or trimethylamine precursors such as eggs, certain fish, or some vegetables.
-
Is TMAU dangerous?
It isn't physically harmful, but the social and psychological impact of the persistent odour can be significant, sometimes leading to anxiety, low self-esteem or social withdrawal.
-
Is TMAU hereditary?
Yes, the primary genetic form is inherited in an autosomal recessive pattern, meaning both parents carry a copy of the altered FMO3 gene, though milder or secondary forms can also occur without a clear genetic cause.
-
Can TMAU be cured or managed?
There is no cure, but dietary changes to reduce trimethylamine-precursor foods, along with certain supplements or short courses of antibiotics to reduce gut bacteria production of trimethylamine, can significantly reduce odour.
-
How is TMAU diagnosed?
Diagnosis involves a urine test measuring trimethylamine levels before and after a choline load, sometimes alongside genetic testing for FMO3 gene variants.
-
How long does management take to show benefit?
Dietary changes can reduce odour within days to weeks, though ongoing dietary and lifestyle adjustment is usually needed long-term to keep symptoms controlled.
-
TMAU vs poor hygiene - what's the difference?
TMAU odour persists despite good hygiene and is linked to specific foods and metabolic processing, whereas odour from hygiene issues typically responds to washing and doesn't have the same dietary trigger pattern.
-
When should I see a specialist about persistent body odour, and how quickly can I be seen privately?
See a doctor if you have persistent unexplained body odour despite good hygiene. NHS metabolic specialist referral can take time; private metabolic or dermatology specialists can often see you within about two weeks.