Trimethylaminuria: When Your Body Insists On Smelling Like Fish
Category: Medical Oddities 15th May 2026
Alas, nature occasionally develops a sense of humour so exquisitely maladroit that it manifests as trimethylaminuria, a metabolic hiccup which makes a person's breath, sweat and urine smell strongly of fish. The cause is straightforward and yet theatrically petty: a deficiency in a liver enzyme known as flavin containing monooxygenase 3, or FMO3, which normally converts the malodorous chemical trimethylamine into an odourless compound. When the enzyme forgets its manners, the trimethylamine goes about its business smelling like an overambitious maritime market.
The trimethylamine itself is not born in the liver but coaxed into being by gut bacteria that munch on choline and other related compounds found in eggs, fish, legumes and soya. Eat the offending things, the microbes get industrious, and your body becomes politely honest about the result. Diagnosis is reasonably modern: doctors measure trimethylamine and its converted product in the urine to confirm the enzymatic failure.
It is rare, yes, and mercifully not life threatening, but it is socially corrosive in the most English way possible. People find it distressing because it invites whispers, awkward ventilation, and the kind of stigma that makes otherwise civilised humans adopt the demeanour of small-minded officials inspecting a lampshade. It also resists simple cosmetic fixes. A dab of perfume will not so much mask the aroma as provide a jolly argument between two competing scents.
Treatment is practical rather than poetic: a low choline diet, careful avoidance of trigger foods, short courses of antibiotics to quiet the bacterial production, and in some cases activated charcoal or copper chlorophyllin to bind the odour. Genetic counselling is offered because the condition tends to run in families. The medical approach is efficient, compassionate and, crucially, utterly devoid of melodrama, which is precisely what sufferers need when the rest of the world prefers melodrama and fresh air.
One finds, oddly, that the condition reveals much about human manners: we are excellent at inventing rules to ostracise one another but slow to invent empathy. Trimethylaminuria is a small biochemical scandal; the proper human response is curiosity, biscuits, and a dash more kindness than one receives at the local health authority.