Fish Odour Syndrome – Trimethylaminuria and Its Health Effects

Having bad breath can be socially embarrassing for you. Bad breath is one of the standard oral problems that people suffer from in their life.

Generally, bad breath is caused due to several reasons. One of them is the consumption of food that has a strong pungent smell like onion and garlic.


Another reason for bad breath is poor oral hygiene. When the food debris is not cleaned in the mouth, oral bacteria ferment it with time and produces characteristic bad smell.

In some instances, Halitosis can also be caused by systemic problems. A rare genetic disorder that may cause bad breath is trimethylaminuria.

Trimethylaminuria is a metabolic disorder of the digestive tract which not only impairs your overall health but affects oral health as well. (1)

Trimethylaminuria produces a volatile compound called trimethylamine which gives this disorder the characteristic fishy odor.

Many factors can cause trimethylaminuria, but most commonly it is associated with the formation of faulty genes inherited from the family members.

Different therapies help to subside the symptoms, but there is no definite cure for trimethylaminuria.

Today’s article highlights this metabolic disorder and draws attention to its potential role in causing oral malodor.

What is trimethylaminuria?

Trimethylaminuria, also called as the fish odor syndrome, is an uncommon condition that is characterized by an unpleasant fishy smell.

It is a metabolic disorder where the body loses its ability to breakdown trimethylamine, a volatile compound that has the characteristic odor. As this compound builds up in the body, the body starts to give off a strong fishy smell through urine, sweat, and breath. (2)

Such a condition adversely affects the quality of life and social interactions. As a result, people with trimethylaminuria often suffer from depression and social isolation.

What causes trimethylaminuria?

Several reasons may case this unusual medical condition. Based on the type of cause, trimethylaminuria is divided into two kinds –  (3)

  • Primary trimethylaminuria – It is a genetic defect inherited as an autosomal recessive trait. Flavin-containing monooxygenase 3 (FMO3) is the responsible enzyme which causes this condition.
  • Secondary trimethylaminuria – Treatment with large doses of diuretic precursors of trimethylamine causes the inability of the liver enzymes to breakdown the chemical compound. As a consequence, this event causes secondary trimethylaminuria.

What are its signs and symptoms?

The symptoms of trimethylaminuria can be present since birth, but they become noticeable later in life, often after puberty.

Typically, the only symptom of trimethylaminuria is a firm unpleasant rotten fish-like odor that may be noticed through –

  • Bad breath
  • Sweat
  • Urine
  • Vaginal fluids

The fishy smell may come and go, but it can be aggravated by stress, certain food items, like eggs, beans, fish, and menstruation cycles.

Does trimethylaminuria affect oral health?

There is no documented adverse effect of trimethylaminuria on the health of the teeth and gums. However, trimethylaminuria is the prime cause to cause oral malodor.

This condition can worsen in cases of poor oral hygiene. The tongue is the primary area of bacterial accumulation. Failure to maintain a clean mouth often becomes a reason for social embarrassment.

How is trimethylaminuria diagnosed?

A rotten fish odor is characteristic of trimethylaminuria. However, a definite diagnosis is made by a physician after ruling out all the possible medical conditions that may have similar symptoms. (4)

  • A thorough medical and family history can help to link the genetic traits.
  • In the case of trimethylaminuria, a urine sample may be taken to analyze and determine the levels of trimethylamine and trimethylamine – N – oxide.
  • Genetic testing is used to differentiate between primary and secondary trimethylaminuria.

What is the available treatment?

A definite cure for trimethylaminuria is not present. However, specific treatment therapies can help to control the symptoms to improve the quality of life.

The first thing to look upon is the eating habits of the patient. Avoid eating food that smells to prevent further complications.

Food items that can aggravate trimethylaminuria and should be avoided are –

  • Eggs
  • Fish especially shellfish
  • Beans
  • Peanuts
  • Cow’s Milk
  • Supplements that contain lecithin

Consultation with your physician and nutritionist can help you in the best way to maintain a healthy diet while avoiding the products mentioned above.

Professional treatments may include a short course of antibiotics to reduce the amount of trimethylamine produced in the gut. An additional supplement of riboflavin (B2) can also help to keep the condition under control. (5)

Other preventive measures that can help to control the symptoms of trimethylaminuria are –

  • Avoid strenuous exercises that cause excessive sweating
  • Stress management – try to adapt activities or routines to relax and calm yourself
  • Take a bath with a slightly acidic soap and shampoo to get rid of the chemical compound from the surface of the skin
  • Use an antiperspirant
  • Wash your clothes regularly as the fabric tends to absorb the moisture and smell from the body

Take away message

Trimethylaminuria is a rare medical disorder. It is a genetic disease that may be inherited by the family members.

Flavin-containing monooxygenase 3 is the prime enzyme that causes the liver’s inability to breakdown trimethylamine, a volatile chemical compound.

Although trimethylaminuria may not affect the body and mouth physically, its only symptom is enough to deteriorate your quality of life.

Presence of a strong fishy odor is not only unpleasant for the person affected by trimethylaminuria but also for the people around him. It is the prime reason for social embarrassment and isolation.


Often people with trimethylaminuria suffer from depression. Mental therapy or counseling can help to cope with the daily struggles. (6)

There is no definite cure for trimethylaminuria, but preventive treatments can help to control the symptoms significantly and improve the quality of life.

To keep your bad breath at bay, good oral hygiene is the right way. A regular oral healthcare routine with quality toothpaste and mouthwash can freshen your breath and help you regain that confidence.


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