What else is it called?

  • Fish malodor syndrome 
  • Fish odor syndrome 
  • Stale fish syndrome 
  • TMAU 
  • TMAuria 

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What causes it?

Trimethylaminuria is caused by a problem in the FMO3 gene. This gene produces the FMO3 enzyme, which breaks down a compound called trimethylamine that is produced in your gut when you eat certain protein-rich food. This process is needed in order to reduce the amount of trimethylamine in the body and to convert it into an odourless molecule. 

 If you have a problem in the FMO3 gene, you will not produce enough of the FMO3 enzyme. Therefore, you will be unable to break down trimethylamine, and this causes it to build up until it is released as a strong, unpleasant odour through your sweat, breath, and urine.  

How common is it?

Trimethylaminuria is a rare disorder and the amount of people who are affected is not known, although around 100 cases have been identified. Some experts believe that the disorder may be under-diagnosed, possibly due to people not seeking medical support for mild symptoms, or some cases being misdiagnosed. 

 It seems that the disorder affects more females than males. Scientists believe that this may be due to higher levels of hormones such as progesterone and estrogen that are more likely to trigger Trimethylaminuria. 

What are the signs and symptoms?

The main symptom of Trimethylaminuria is a strong odour that may be described as smelling like rotten fish, eggs, rubbish, or urine. The smell is usually noticeable in your sweat, urine, and breath. Females may also experience the smell from their vagina.  

There are reports that suggest the symptoms of the disorder may become worse during puberty. Although Trimethylaminuria may present throughout your life, in a number of cases the smell can fluctuate in its intensity, which means that the smell may be less noticeable at times. For women, the smell can become stronger before and during menstruation. 

Apart from a strong odour, there are no other symptoms of this disorder and most people affected are generally healthy. The disorder has no effect on life expectancy.

How is it diagnosed?

Diagnosis cannot be completed based on smell alone. A specialised urine test will be required to measure the amount of trimethylamine in your body. You may also be asked to take supplements and keep samples of your urine over a number of days in order to verify that Trimethylaminuria is the cause. 

Your medical team may also conduct genetic testing to confirm diagnosis of the disorder. 

Many other, more common, disorders and conditions also give off a strong odour, including urinary tract infections, bacterial vaginosis, gum disease, or body odour. Your medical team will have to rule out these possibilities first before diagnosing you with Trimethylaminuria. 


Can it be treated?

There is currently no cure for Trimethylaminuria. However, there are a number of steps you can take to improve the symptoms. These include: 

  • Avoiding certain foods, for example cow’s milk, some seafood, eggs, beans, peas, peanuts, and liver 
  • Avoiding strenuous exercise. Instead, adopt gentle exercise regimes that you can do regularly 
  • Reducing stress in your life, as stress has been shown to trigger the disorder 
  • Washing your skin with a slightly acidic soap and shampoo that has a pH of between 5.5 and 6.5 
  • Using deodorant regularly to reduce sweat 
  • Washing your clothes regularly 

Before you make any changes to the foods you eat, it is very important to consult a dietician to ensure that you have a healthy, balanced diet that also helps you to successfully manage your disorder. You may also be offered supplements by your medical team. 

 Although Trimethylaminuria does not affect your physical health, it has been known to take a toll on mental health. Many people with this disorder feel embarrassed and isolate themselves, or they may develop mental issues such as depression and anxiety. It is important that you inform your medical team if you do feel this way. You are entitled to support that will help you to cope with your disorder. 

Do my family need to be tested?

Trimethylaminuria is inherited from both parents in an autosomal recessive inheritance pattern. This means that both parents are carriers of the disorder through their genes.  

All genes come in pairs. Carriers of Trimethylaminuria have one working FMO3 gene and one faulty gene. Children inherit one gene from each parent to make their pair. Whether you have Trimethylaminuria depends on the genes you inherit: 

  • There is a 50% chance that the child will inherit one faulty and one working gene, which means they will also be a carrier. 
  • There is a 25% chance that the child will inherit two working genes and not inherit or carry the faulty gene. 
  • There is a 25% chance that the child will inherit two faulty genes, which means they will have Trimethylaminuria. 

If you think you, or somebody in your family, may have Trimethylaminuria, or that you may be a carrier, contact your medical team who may refer you for genetic testing. 

Relevant Organisations


References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing [Resource Library No: TXM001]. 

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