As silly as it may sound, Fish Odour Syndrome, also known as Trimethylaminuria, is a genetic illness, first identified in 1970 which causes its sufferers to smell of rotten fish. This is not an early April Fools' joke, it is a real but rare illness. Only about 200 cases have been identified, however it is suspected that there are many more. Often patients do not realise that they have a disease, or are too ashamed to come forward.


To be blunt, you smell of rotting fish. The time at which the disease declares itself varies. It may happen in infancy, during childhood or puberty. In some cases patients have not become symptomatic until adulthood.

Who catches it?

It's a recessive genetic disease, so if you spot someone smelling of fish, do not be afraid to talk to them: it is not contagious, you're either born with it or you're not. Currently the incidence in various populations are not known. It has been associated with some other genetic disorders, such as Noonan's and Turner's Syndrome and Prader-Willi Syndrome.


A precise diagnosis may be made by measuring levels of trimethylamine in the patient's urine.


The disease is believed to be caused by a gene carried on chromosome 1. This gene controls the production of an enzyme (known as flavine mono-oxydase) that degrades a chemical known as trimethylamine into trimethylamine N-oxide. The former is a strong, foul smelling substance produced by naturally occurring bacteria in the intestine, whereas the latter is odourless. Inside a normally functioning person trimethylamine is broken down mainly in the liver. A person suffering from the disease does not possess an enzyme capable of breaking down the chemical effectively and trimethylamine is secreted in sweat, urine and breath.

Long term effects

From a purely physiological point of view the disease is harmless, and there are no further ill-effects, apart from the unpleasant smell. In real life of course there are far more serious psychological effects. Social exclusion often leads to low self esteem, anxiety and depression. Sufferers often isolate themselves, leaving home only when necessary and choose jobs where they will be on their own. It is not unknown for victims to smoke heavily to cover up the smell.


There is no long term cure. Antibiotics may be taken in some cases to limit the numbers of the bacteria responsible for producing trimethylamine. Another solution is to restrict patients' intake of choline, which is transformed by the bacteria into trimethylamine. Choline can be found in products such as egg yolk, kidney, liver, peas and salt water fish. Not all patients respond to diet changes though. Because it is often found in connection with other diseases and because the disease is not well known, treatment can be complex.


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