If Your Breath Smells Like This, Have Your Kidneys Checked Immediately

Don't dismiss this surprising symptom as bad oral hygiene.

Bad breath can be the source of embarrassment and frustration, making you self-conscious with every exhalation. And while most of the time this unfortunate symptom can be treated with improved oral hygiene—including brushing, flossing, and getting regular teeth cleanings— sometimes the root cause is something completely unrelated to your dental habits.

One new study has found that in some rare cases, a particular brand of bad breath can signal a serious kidney condition. In fact, some experts say that if your breath smells like this one thing, you should have your kidneys checked by a doctor immediately. Read on to find out what to look out for, and how to help ease your symptoms once you've noticed the problem.

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If your breath smells like fish, it could be due to kidney failure.

young man checks for bad breath by holding hand out in front of mouth and breathing

If you've noticed that your breath—or your sweat or urine, for that matter—smell like rotting fish, it could be the result of kidney failure, a new study published in the quarterly medical journal, Hippokratia, has found.

This disorder is known as trimethylaminuria or fish odor syndrome. "In trimethylaminuria, the body is unable to turn a strong-smelling chemical called trimethylamine–produced in the gut when bacteria break down certain foods–into a different chemical that doesn't smell," explains the U.K.'s National Health Service (NHS).

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There are other possible causes of this symptom.

Woman Sitting Down Talking to Her Doctor Stop Lying to Your Doctor

Trimethylaminuria is not frequently associated with renal failure, and the Hippokratia study is the first of its kind to link the two conditions. However, in that particular case study, the researchers found that one 28-year-old suffered from fish odor syndrome as a result of his kidney disease, ultimately getting relief from the syndrome only after having a kidney transplant.

In other cases, fish odor syndrome can be caused by mutations in the FMO3 gene, excessive protein consumption, liver disease, an increase in certain gut bacteria, poor hygiene, gingivitis, and more. Some women with a faulty FM03 gene experience increased symptoms at the start of menstruation, or when taking oral contraceptives.

Diagnostic tests, usually conducted by urine sample, can help you determine whether your symptoms are the result of fish odor syndrome or from some other cause.

The condition is relatively rare.

Doctor talking to woman with serious tone

Though there have been countless anecdotes of trimethylaminuria throughout medical history, the syndrome was first reported in literature around 1970. Only a few hundred cases have been documented since.

This makes it an exceptionally rare disease—meaning that even your doctor may be unaware of it. "Some physicians might be unaware of the disorder, not recognizing the symptoms and potentially being unable to distinguish them from other conditions that result in an unpleasant body odor," explains a study published in the medical journal Drug Discovery Today.

For this reason, if your concerns about the symptom are initially dismissed, it's important to self-advocate until you're satisfied with your care.

However, it can take a toll in many areas of a person's life.

A teenage girl with dark hair looks out a window with a sad look on her face.

Unfortunately, even when the symptom doesn't indicate a serious underlying cause, it can still trigger serious psychological distress to those who suffer from it. "The strong body odor can interfere with many aspects of daily life, affecting a person's relationships, social life, and career," reads the Hippokratia study. "Some people with trimethylaminuria experience depression and social isolation as a result of this condition."

The researchers behind the Drug Discovery Today study confirmed these same findings, adding that "although the disease is considered benign, its psychological burden can be devastating." They warn that many patients suffer from "strong feelings of shame, embarrassment, social isolation and even suicidal tendencies, among others."

For this reason, experts recommend a two-pronged approach to treatment, after ruling out serious causes like kidney disease. First, you should consult your doctor for tips on dietary changes that can lessen symptoms, and second, speak with a counselor who can help assess and address your emotional wellbeing.

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Lauren Gray
Lauren Gray is a New York-based writer, editor, and consultant. Read more
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