Fish Odour Syndrome

Fish Odour Syndrome

Trimethylaminuria, or fish odour syndrome, is a rare condition that results in the body excreting trimethylamine, a compound found in certain foods, through the urine, breath or sweat. This has a fishy odour. There aren’t any physical symptoms associated with the condition, but it can cause social problems for the sufferer because of the smell. Antibiotics may help ease the condition, and changes to a person’s diet could help, for example restricting intake of foods that contain trimethylamine or choline, such as eggs, liver, peanuts and beans.


Trimethylaminuria (TMAU), more commonly known as fish odour syndrome or fish malodour syndrome, is a rare metabolic disorder. This condition causes the body's ability to properly metabolise trimethylamine (TMA), an organic compound found in certain foods, into trimethylamine oxide (TMAO) to malfunction. Trimethylamine builds up and is released through the person's sweat, breath and urine giving off a strong fishy odour.

Causes and Symptoms

There are two types of this condition: TMAU 1 and TMAU 2. TMAU 1 is an inherited genetic disease caused by a faulty recessive gene. This faulty gene affects the FMO3 enzyme in the liver whose job is to metabolise trimethylamine (TMA) creating a build up of TMA which leads to the nasty body odour.

In the case of TMAU 2 the FMO3 activity in the liver is unable to fully oxidise all the TMA entering the body. This may be due to something blocking the enzyme or because excessive amounts of TMA are entering the body from the gut which may be caused by bacterial overgrowth.

In both cases TMA accumulates creating the odour.

The mental effects of TMAU

TMAU is a potentially distressing condition leading to depression, and other psychological problems, caused by its antisocial characteristic of unpleasant body odour which could result in social exclusion. Signs of the condition can show at various ages from infancy to adulthood depending mainly on whether the disorder is inherited or acquired.

Diagnosis and Treatment

If you think you may have this condition you should contact your GP who may then refer you for a urine test. However, not all GPs know about the condition as it is very rare. The urine test will help to determine if you have Trimethylaminuria. Diagnosis for TMAU 1 is also possible through gene sequencing which is done with a blood test.

The disorder is very rare and research is being conducted on it. There is a variety of antibiotics and probiotics that can help ease the condition. Eating a diet low in choline can help but choline is found in many common foods so could prove quite restrictive. It is found particularly in eggs, wheat germ and some meats. You should consult your doctor before altering your diet.