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Trimethylaminuria : What Is Fish Odor Syndrome & What Makes A Person Smell Like Fish Or Rotten Eggs?

What is Trimethylaminuria (TMAU) or Fish Odor Syndrome?

Trimethylaminuria is a rare and intriguing medical condition that causes the saliva, breath, sweat and pee to smell like rotten eggs or rotten fish.(1) Some individuals suffer from trimethylaminuria because of defective genes which also affect their metabolism. Other causes of trimethylaminuria can be certain medications and illnesses.

Trimethylaminuria isn’t necessarily a fatal major health condition; however, it greatly affects the patient psychologically. Patients suffering from trimethylaminuria have difficulty in coming to terms with this condition and living a normal life and as a consequence suffer from social and psychological issues.(1) There is no cure for trimethylaminuria; however, making lifestyle modifications like changing soaps and diet, keeping the stress levels under control and using certain lotions helps in alleviating the symptoms.(3, 4)

What is Trimethylaminuria (TMAU) or Fish Odor Syndrome?

What are the Causes of Trimethylaminuria?

The body of the patient suffering from trimethylaminuria is not able to process trimethylamine, which is a foul smelling chemical. The intestines produce trimethylamine upon consuming certain foods, such as eggs legumes and liver. An enzyme named flavin-containing monooxygenase 3 (FMO3) is normally produced by the body which processes the chemical trimethylamine. However, when there are some problems with this enzyme and it doesn’t work, then it results in increased levels of trimethylamine causing foul smell of the pee, sweat, and breath.(1, 3, 4)

The cause of trimethylaminuria in some patients is inherited metabolic condition that prevents the enzyme from metabolizing trimethylamine. This type of trimethylamine is known as primary trimethylaminuria and it develops when there is some problem with the FMO3 gene, which carries instructions about manufacturing the FMO3 enzyme. In the absence of correct instructions, the body is unable to produce the effective enzyme to combat trimethylaminuria.

Who is at Risk for Trimethylaminuria?

As mentioned before, trimethylaminuria or fish odor syndrome is an extremely rare disease and only a few hundred cases have been reported in three decades. Females are at higher risk for suffering from trimethylaminuria than males.

Who is at Risk for Trimethylaminuria?

Why Do Some People Have Trimethylaminuria When Their Parents Don’t?

When this gene from your parents is passed on to the patient, he/she gets two copies of each gene. When suffering from primary trimethylaminuria, then it is because each parent has single copy of the altered FMO3 gene.(1) This altered gene is not able to give instructions for producing the FMO3 enzyme.

With the absence of this enzyme, the body of the patient cannot process the trimethylamine which is the foul smelling chemical. The parents of the patient do not suffer from trimethylaminuria as they both have one altered and one normal gene. The parents will have the changed gene; however, will not suffer from symptoms, as trimethylaminuria develops when there are two defective genes.

Another type of trimethylaminuria developed by patients is secondary, transient or acquired trimethylaminuria.(2) Patients suffering from this type of trimethylaminuria carry FMO3 enzymes; however, there is something which does not allow the enzyme to completely process the trimethylamine.(2) Patients have secondary trimethylaminuria when they are suffering from liver failure or those who take choline supplements for treatment of Huntington’s or Alzheimer’s disease. Choline is a vital nutrient present in eggs, vegetables, beans, nuts, fish and meats.

What are the Symptoms of Trimethylaminuria (Fish Odor Syndrome)?

Patients suffering from trimethylaminuria or fish odor syndrome, emanate a strong and bad smell, which becomes more obvious when under stress or after exercise. Females suffer from more severe symptoms of trimethylaminuria before and during their menstrual cycle and when going through menopause and after taking oral contraceptives.

Patients who have inherited trimethylaminuria commonly struggle with substantial social and psychological issues. The symptoms of trimethylaminuria worsen during puberty, which makes the preteen or teenage kids more prone to bullying or getting teased. A few children suffering from trimethylaminuria respond to this bullying by becoming disruptive and aggressive. Trimethylaminuria affects the patient’s behavior and wellbeing in the following ways:

Trimethylaminuria patients have great difficulty in developing or maintaining any type of relationship.(2)

Trimethylaminuria patients also avoid social gathering and meeting people, as they are keenly embarrassed about how they smell. Social isolation can cause loneliness, frustration and depression.(2)

Rarely patients suffering from trimethylaminuria can show signs of suicide and paranoia.(2)

Can Patients Suffering Trimethylaminuria Smell Themselves?

Yes indeed, just like the normal sweat or body odor, individuals with trimethylaminuria or fish odor syndrome can notice how they smell. However, just like the normal body sweat or odor, the individuals with trimethylaminuria get used to how they smell and may not react to it, as much as those people who are around them.

How to Diagnose Trimethylaminuria?

The diagnosis of trimethylaminuria is made by measuring the quantity of trimethylamine in the patient’s urine.

Is There Any Cure For Trimethylaminuria?

There is no cure for trimethylaminuria be it primary or inherited.(3, 4) However, changing diet, some medications and the hygiene routine can help in masking or reducing the symptoms of trimethylaminuria.

What Foods to Avoid When Suffering From Trimethylaminuria?

Doctors recommend avoiding the following foods: Cauliflower, cabbage, eggs, beans, liver, Brussels sprouts, soya products, broccoli, peanuts, peas, milk derived from wheat-fed cows; fish oil supplements and seafood. Fresh-water fish can be eaten.(3)

Removing these foods from the diet can decrease quantity of essential nutrients, such as folate and choline. So, it is important that your doctor uses other methods to ensure that you have sufficient folate and choline. Patients suffering from trimethylaminuria who are breastfeeding or pregnant should not avoid foods containing choline. In such cases, seek your doctor’s advice for other ways to reduce the symptoms of trimethylaminuria.

If Someone Smells Like Fish After Consuming Fish, Does It Mean They Have Trimethylaminuria?

If after eating fish, you smell like it, then it need not mean that you are suffering from trimethylaminuria, but it can mean that there is development of transient fish like bad breath after consumption of fish.

What are the Medications Used for Treating Trimethylaminuria?

The doctor can prescribe a small course of antibiotics to decrease the gut bacteria so there is less amount of trimethylamine in the gut.(1, 2) Probiotics are also advised to cut down the quantity of trimethylaminuria and for better gut health.

Things That Help With the Symptoms of Trimethylaminuria

Doctors also recommend using acidic lotions and soaps with a low-pH to decrease the odor.(3) Other methods to cut down of the amount of sweating is reducing the stress levels and avoiding rigorous exercise.(3) Frequently changing clothes and sheets into fresh ones also helps with the symptoms of trimethylaminuria or fish odor syndrome.(3)

What is the Prognosis of Trimethylaminuria?

TMAU or trimethylaminuria cannot be cured, but can be managed.(3) When having primary trimethylaminuria, lifestyle modifications make difference in the symptoms. If the cause of trimethylaminuria is medications, then seek advice of your doctor to change the meds.

As trimethylaminuria impacts the mental health of the patient it is important to seek mental health support to manage the psychological symptoms of trimethylaminuria, such as depression, low self esteem, and social isolation.


It is important that the patient understands that trimethylaminuria is a condition that has occurred to them and they are in no way responsible for it. It is through accepting this condition and managing its symptoms that patients can live a better and productive life. It is important to have a good support system and also seek counseling to combat the mental health symptoms occurring as a result of trimethylaminuria.(3)


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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:October 15, 2022

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