Is there a disease where you always smell bad? The truth about TMAU

September 22, 2025 •

4 min read

Trimethylaminuria (TMAU), often called 'fish odor syndrome,' is a metabolic disorder where the body cannot properly break down a foul-smelling chemical called trimethylamine. For those asking, "Is there a disease where you always smell bad?", this rare genetic condition provides a definitive and often life-altering answer.

Quick Summary

Trimethylaminuria (TMAU) is a rare metabolic disorder that prevents the body from breaking down a chemical compound called trimethylamine, causing it to build up and be released through sweat, breath, and urine, creating a persistent, fishy odor.

Key Points

Trimethylaminuria (TMAU) is a real disease: Yes, a disease exists that causes a persistent, bad smell, most famously trimethylaminuria, or 'fish odor syndrome'.
Caused by a genetic enzyme deficiency: Primary TMAU results from a defect in the FMO3 enzyme, which is needed to break down the smelly chemical trimethylamine.
Odor comes from sweat, breath, and urine: The unprocessed chemical is released from the body through various excretions, causing a pungent odor.
Not a hygiene issue: Unlike common body odor, TMAU is not caused by poor hygiene and requires specific medical management, not just more washing.
Diagnosis requires a urine test: A doctor can confirm TMAU by testing a patient's urine, especially after consuming choline-rich foods.
Symptoms are manageable: Management involves dietary changes, special soaps, supplements, and sometimes antibiotics.
Psychological impact is significant: The persistent odor can lead to social isolation, anxiety, and depression, making mental health support important.

What is trimethylaminuria (TMAU)?

Trimethylaminuria is a metabolic disorder characterized by a strong, unpleasant body odor often described as smelling like rotten fish. This happens when the body is unable to process trimethylamine (TMA), a chemical with a powerful odor, which is produced by gut bacteria after digesting certain foods rich in choline.

The FMO3 enzyme and metabolic pathway

At the heart of TMAU is a malfunctioning enzyme called flavin-containing monooxygenase 3 (FMO3). Normally, this enzyme converts foul-smelling TMA into an odorless compound called trimethylamine N-oxide (TMAO), which the body then excretes without issue. However, in individuals with a deficient or dysfunctional FMO3 enzyme, TMA accumulates in the body and is released through sweat, breath, and urine, causing a distinctive and socially challenging odor.

Primary vs. secondary trimethylaminuria

There are two main types of TMAU:

Primary TMAU: This is a genetic form of the disorder caused by mutations in the FMO3 gene, inherited in an autosomal recessive pattern. This means a person must inherit a mutated gene from both parents to have the condition. However, carriers with only one faulty gene may experience mild or temporary episodes of odor.
Secondary TMAU: Also known as acquired TMAU, this form can arise from other factors that overwhelm a normal FMO3 enzyme. Causes can include:
- Liver or kidney disease
- An overgrowth of TMA-producing bacteria in the gut
- Certain dietary supplements, such as high doses of choline or carnitine
- Temporary symptoms in some healthy women during menstruation

Diagnosis of trimethylaminuria

Since the odor can be inconsistent and is highly subjective, relying on smell alone is not sufficient for a diagnosis. A proper diagnosis is crucial for managing the condition and is typically achieved through a specific urine test.

A urine sample is collected, sometimes after the individual consumes a choline-rich meal (e.g., marine fish) to challenge the FMO3 enzyme.
The ratio of TMA to the processed TMAO in the urine is measured.
Genetic testing can also be performed to identify mutations in the FMO3 gene, confirming a diagnosis of primary TMAU.

Management and treatment of TMAU

While there is currently no cure for TMAU, symptoms can often be managed effectively through a combination of lifestyle changes and medical interventions.

Dietary modifications

Avoid certain foods: Reduce or eliminate consumption of foods containing high levels of choline, TMA, and its precursors, including marine fish, eggs, organ meats (liver, kidneys), legumes (peas, beans), and cruciferous vegetables like broccoli and cauliflower.
Consult a dietitian: Working with a registered dietitian is important to ensure a balanced diet while restricting certain nutrient-rich foods.

Hygiene practices

Use low-pH soaps: Because trimethylamine is alkaline, using soaps with a pH between 5.5 and 6.5 helps make the chemical less volatile, reducing its odor.
Wash frequently: Regular washing of skin and clothing is recommended.

Medications and supplements

Antibiotics: In some cases, low-dose antibiotics can help suppress the intestinal bacteria responsible for producing TMA.
Activated charcoal and copper chlorophyllin: These supplements can bind to TMA in the gut, reducing its absorption into the body.
Riboflavin (Vitamin B2): Supplements may be used to enhance any residual FMO3 enzyme activity.

Psychological support

Living with the social stigma of a persistent body odor can cause significant emotional distress, including anxiety, depression, and social isolation. Mental health support can help individuals cope with the psychological effects of the condition.

Comparing TMAU with other odor-related conditions


Condition	Cause	Odor Description	Key Diagnostic Factor
Trimethylaminuria (TMAU)	Genetic deficiency of FMO3 enzyme or secondary factors leading to high trimethylamine.	Distinctive 'rotten fish' or garbage-like smell.	Urine test measuring trimethylamine and TMAO ratio.
Bromhidrosis	Bacterial breakdown of sweat, particularly from apocrine glands.	Typically a strong, offensive 'body odor,' exacerbated by sweat.	Clinical diagnosis based on odor, potentially ruled out by ruling out systemic conditions.
Diabetic Ketoacidosis	High ketone levels in uncontrolled diabetes.	Fruity or sweet-smelling breath.	Blood and urine tests measuring glucose and ketone levels.
Liver Disease	Failure to properly filter toxins.	Often described as a musty, ammonia, or bleach-like smell.	Blood tests measuring liver function.
Kidney Disease	Inability to filter waste products effectively.	Ammonia or urine-like smell on the breath and skin.	Blood tests measuring kidney function.

Broader implications of chronic body odor

Beyond TMAU, many other conditions can cause chronic or unusual body odors, indicating underlying health issues. Persistent odor should always prompt a medical evaluation to rule out other serious conditions like diabetes, liver or kidney disease, and certain infections. An accurate diagnosis is the first step toward effective management and improving one's quality of life. For more detailed information on genetic disorders, including TMAU, consult the National Human Genome Research Institute website.

Conclusion: Seeking answers for persistent odor

For those who have struggled with persistent, unexplained body odor, the answer to "Is there a disease where you always smell bad?" is yes, and it is most commonly trimethylaminuria. It is not a reflection of poor hygiene, but rather a complex metabolic issue. By understanding the causes, seeking a proper diagnosis, and implementing personalized management strategies, individuals with TMAU can effectively control their symptoms and reclaim their social and personal lives.

The importance of accurate diagnosis

The correct diagnosis is vital. Without it, individuals may misattribute the odor to poor hygiene, leading to self-esteem issues, anxiety, and social isolation. A healthcare provider can help differentiate TMAU from other, more common, or more serious conditions with similar symptoms, ensuring the right path to management.

Frequently Asked Questions

Yes, for individuals with trimethylaminuria (TMAU), consuming foods high in choline and its precursors, such as marine fish, eggs, beans, and certain vegetables, can exacerbate the production of foul-smelling trimethylamine.

Currently, there is no cure for trimethylaminuria, especially the primary genetic form. However, symptoms can be effectively managed through a combination of dietary control, hygiene adjustments, and sometimes medication.

Yes, stress can trigger the apocrine sweat glands, which are found in areas like the armpits and groin. The sweat from these glands, when combined with skin bacteria, can produce a more noticeable odor.

TMAU is a metabolic disorder resulting from the body's inability to break down trimethylamine, causing a fishy or garbage-like smell. Bromhidrosis is a strong body odor caused by the bacterial breakdown of normal sweat on the skin's surface and is more common.

A doctor can diagnose trimethylaminuria (TMAU) with a specialized urine test that measures the ratio of unmetabolized trimethylamine to its odorless derivative. This can be done after consuming a choline-rich meal to provoke the odor.

Yes, liver or kidney disease can cause a change in body odor. When these organs fail to properly filter toxins from the body, waste products can build up and be excreted through the breath and sweat, causing an ammonia or bleach-like smell.

Yes, primary trimethylaminuria is a genetic condition inherited in an autosomal recessive pattern. A person must receive a mutated FMO3 gene from both parents to have the disorder. Acquired (secondary) TMAU is not inherited.