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  Oct 17, 2018

Fish Odour Syndrome (Trimethylaminuria)

Fish odour syndrome, also known as trimethylaminuria, is a disorder that causes a strong odour in the urine, sweat and breath of affected individuals, described as similar to rotting fish.

This odour is caused by a chemical called trimethylamine, which the body is usually able to break down into another, less pungent substance. However, people affected by fish odour syndrome lack this ability.

It is most commonly a genetic disorder present from birth, however some people start noticing symptoms in adulthood and do not possess a gene defect. More women than men are affected, which is speculated to be a result of the female hormones, estrogen and progesterone.


The main presenting symptom of fish odour syndrome is the fowl smelling body odour coming from the sweat, urine and breath and it doesn’t seem to cause any other symptoms beyond the bad smell.

Many people who suffer from the syndrome also experience psychological effects due to the impact on their daily life. Depression and social isolation are common, affecting personal life and interactions with other people.  

Causes and Triggers

The most common cause of fish odour syndrome is a defect in the FMO3 gene, which inhibits the body’s process to break down trimethylamine. It can be inherited from a parent with the same gene defect and children are able to take a test to see if they are affected.

The severity of the condition does not stay constant and can change dramatically throughout different life stages. It is usually worse during puberty and around the time of menstruation and menopause for females. In addition, certain foods lead to the production of trimethylamine and can worsen the syndrome, such as:

  • Animal products (milk, eggs)
  • Peanuts
  • Soy products
  • Meat products (liver, kidney)
  • Seafood
  • Certain vegetables (brussel sprouts, broccoli, cabbage, cauliflower, peas, beans)

Diagnosis and Management

When fish odour syndrome is suspected due to the presenting symptoms, it can be diagnosed using a test that determines the ratio of trimethylamine to trimethylamine N-oxide in the body. This helps to demonstrate if the body is converting the smelly substance to the normal one as usual.

Currently there is no specific treatment or cure for fish odour syndrome, but those affected can manage the condition using several recognized techniques. Using a slightly acidic soap (pH 5.5-6.5) can effectively remove traces of trimethylamine from skin and hair, helping to reduce associated odour. Additionally, recognising the foods that worsen the condition and changing the diet accordingly can lessen the impact.

It is important for individuals to receive sufficient psychosocial help to assist them in daily life and address the issues that fish odour syndrome places on their wellbeing.

Some medications have been used, including antibiotics and laxatives to reduce the production of trimethylamine in the stomach. While these may be of benefit for some individuals, they are not currently recommended for routine use.