For some people with a rare condition, their body produces a fish-like smell. That rare condition is known as trimethylaminuria.

People who live with it may find themselves feeling self-conscious because their breath and urine have a strong fish odor.

This article will offer background information about trimethylaminuria, what causes this rare disorder, and how you can treat it and find support.

Trimethylamine (TMA) is a chemical compound that smells like rotting fish. It’s produced in the gut, often from certain dietary amines. This compound is often associated with atherosclerosis and severe cardiovascular disease.

When a person’s body is unable to break down TMA, trimethylaminuria can develop. As this TMA builds up in the body, it causes the body to give off a strong odor.

Trimethylaminuria is an uncommon genetic disorder. The exact number of people who have it is unknown.

More than 100 cases have been reported in medical literature, but some clinicians believe it’s underdiagnosed. This is because trimethylaminuria often goes unrecognized even by healthcare professionals, and people with mild symptoms don’t always seek medical help.

How to pronounce trimethylaminuria

Here’s how you pronounce this condition: tri-meh-thuh-la-muh-nyur-ee-uh.

Other names for it include:

  • stale fish syndrome
  • fish odor syndrome
  • fish malodor syndrome
  • TMAU
  • TMAuria

Trimethylaminuria is typically caused by mutations to the FMO3 gene.

Typically, FMO3 is responsible for the production of an enzyme that breaks down TMA into an odorless molecule. When this enzyme is not produced or its activity is reduced, TMA can build up in the body. The excess TMA is then released through bodily fluids like sweat and urine.

Mutations to FMO3 are generally inherited in a recessive pattern, meaning both parents are at least carriers of one copy of the mutated FMO3 gene. Carriers may have no signs of trimethylaminuria or mild symptoms, or temporary fish odor episodes.

Even without mutations to FMO3, some people may experience trimethylaminuria from an intake of large doses of TMA or products that increase TMA production.

The most common sign and symptom of trimethylaminuria is a strong fish-like odor. It may be released in:

  • sweat
  • breath
  • urine
  • reproductive fluids

The fish-like odor may vary in consistency or stay at a strong level. It may worsen with exercise or stress, since those can increase how much you sweat.

People who menstruate may experience stronger fish scents just before and during their periods. The fish odor can also be stronger when taking birth control pills or as a person approaches menopause.

While trimethylaminuria does not typically have any other physical symptoms besides a fishy odor, it can cause people to socially isolate themselves and lead to depression.

No cure currently exists for trimethylaminuria. However, you may be able to manage it by carefully choosing what foods you consume.

Foods to avoid include those high in trimethylamine N-oxide and choline. They increase the amount of TMA in the body.

Trimethylamine N-oxide is present in seafood, including:

  • fish
  • squid
  • octopus
  • crabs
  • lobsters

Foods with choline include:

  • eggs
  • beans
  • liver
  • kidney
  • peanuts
  • broccoli

Additionally, it’s important to avoid milk from wheat-fed cows. The milk may contain high amounts of TMA. Supplements containing lecithin can also make the fish odor worse.

Other ways to address trimethylaminuria

It may also be possible to reduce TMA levels by taking:

  • a small dose of antibiotics
  • a laxative to speed up digestion
  • certain supplements, like activated charcoal and copper chlorophyllin
  • riboflavin (vitamin B2) to help increase any existing FMO3 enzyme activity

You can consult your doctor or healthcare team about the right dosage for any of these medications or supplements.

You may also wish to try using soaps and lotions with a pH level of 5.5 to 6.5. These may make it easier to wash off TMA from the skin.

Since intense exercise and high levels of stress can increase sweat levels, people with trimethylaminuria may want to avoid these when possible.

People who have trimethylaminuria may feel isolated or develop depression. To find support and get help in dealing with this condition, you can:

  • Reach out to a therapist: Virtual therapy is available for people who prefer it. Consider these 10 best online therapy services.
  • Talk with a registered dietitian: They can work with you to develop a balanced, nutritious diet that minimizes symptoms.
  • Join a support group for people with trimethylaminuria: Local support groups may not be as easy to find because this is a rare condition. However, online communities specific to people impacted by trimethylaminuria can offer a chance to connect with others who understand what you’re going through. Those might include online sites like RareConnect, which can help people find those connections.

Trimethylaminuria is a rare condition that produces a fish-like odor. Experts believe a mutation to the FMO3 gene causes it. This mutation leads the body to not being able to break down the chemical compound trimethylamine (TMA).

Although there’s no cure for trimethylaminuria, changes to your eating habits may help manage it. Therapy and online support groups can also provide important emotional support if you find that your mental and social health are impacted by the condition.

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