A persistent, unpleasant body odor, particularly one resembling feces, can be deeply distressing. While many assume the cause is poor hygiene, a chronic fecal-like odor (often termed Fecal Body Odor or FBO) is a recognized medical complaint pointing to an underlying biological or metabolic issue. This odor is not typically a result of a lack of cleanliness, but rather a complex process involving the body’s digestive system, bacterial balance, or metabolic pathways. Understanding the potential origins of the smell is the first step toward finding an accurate diagnosis and treatment plan.
Identifying the Source of the Odor
Before investigating internal causes, it is necessary to rule out localized, external factors that can mimic a pervasive fecal smell. A primary source is minor anal leakage, or fecal incontinence, which involves the involuntary release of small amounts of mucus or stool. Conditions like hemorrhoids or weakened anal sphincter muscles can prevent the anus from sealing completely, allowing residue to accumulate on the skin. This residue then interacts with natural bacteria, causing a distinct odor.
Localized skin conditions in warm, moist areas, such as the groin or skin folds, also contribute to this type of odor. Intertrigo, an inflammatory rash caused by friction and trapped moisture, is a common example. If intertrigo develops a secondary bacterial or fungal infection, it can produce a foul-smelling discharge that may be perceived as fecal. Addressing these localized issues involves meticulous hygiene, specialized topical treatments, and ensuring the affected areas remain dry and breathable. Residual fecal matter from incomplete wiping or clothing that traps moisture can also lead to a strong, lingering scent.
Digestive System Contributions to Odor
If external factors are ruled out, the digestive tract is often the next focus, as gut bacteria produce a wide range of volatile organic compounds (VOCs). A significant contributor is Small Intestinal Bacterial Overgrowth (SIBO), where excessive bacteria colonize the small intestine. This overgrowth leads to the premature fermentation of undigested carbohydrates and proteins, creating gases such as hydrogen, methane, and hydrogen sulfide.
Hydrogen sulfide is responsible for a characteristic “rotten egg” or foul smell, while methane-producing organisms are associated with a heavier odor. These gases are not only expelled as flatulence but are also absorbed into the bloodstream through the intestinal wall. Once in circulation, these foul-smelling VOCs are released through the breath and sweat glands, causing a pervasive body odor.
Malabsorption disorders also generate strong odors due to the failure to process specific nutrients. In lactose intolerance, the lack of the lactase enzyme means milk sugar passes undigested into the colon, where bacteria ferment it into gas. Similarly, in untreated Celiac disease, damage to the small intestine lining leads to poor absorption of fats and nutrients. This results in steatorrhea, characterized by pale, greasy, and intensely foul-smelling stools, as undigested fats ferment in the lower bowel.
Systemic and Metabolic Conditions
A persistent fecal-like body odor can signal a rare metabolic condition where the body cannot properly break down certain compounds. The most well-known of these is Trimethylaminuria (TMAU), often called “fish odor syndrome,” though the odor is sometimes described as urine-like, rotten garbage, or fecal. Primary TMAU is a genetic disorder caused by a defect in the FMO3 enzyme, which is primarily produced in the liver.
This enzyme converts the foul-smelling chemical trimethylamine (TMA), produced by gut bacteria from choline-rich foods, into its odorless form, trimethylamine N-oxide (TMAO). When the FMO3 enzyme is deficient or dysfunctional, TMA builds up in the body and is excreted through sweat, breath, and urine. The intensity of the smell can fluctuate based on diet, stress levels, and hormonal changes, which can make diagnosis challenging.
Systemic conditions involving organ failure can also alter body odor due to the accumulation of toxins the body can no longer filter. Advanced liver disease can lead to fetor hepaticus, causing a distinct breath odor often described as musty, sweet, or sometimes fecal. This smell is caused by the liver’s inability to filter sulfur-containing compounds, such as dimethyl sulfide, from the bloodstream. Severe kidney failure results in uremic fetor, characterized by an ammonia or urine-like odor. This occurs when the kidneys fail to clear urea, which is then broken down into ammonia in the saliva and detected on the breath.
Seeking Medical Guidance and Diagnosis
Given the varied causes of persistent malodor, seeking professional medical guidance is necessary for resolution. The initial consultation should be with a primary care physician, who can then refer a patient to specialists such as a gastroenterologist for digestive issues or a geneticist or dermatologist for systemic conditions. Preparing for this appointment involves maintaining a detailed log of symptoms, noting the time of day the odor is strongest and any correlation with specific foods or stress.
Diagnosis involves specific laboratory tests tailored to the suspected condition. For digestive issues like SIBO, a non-invasive breath test measures the levels of hydrogen and methane gas exhaled after consuming a sugar solution, indicating bacterial overgrowth.
To diagnose TMAU, physicians use a specialized urine test measuring the ratio of trimethylamine to its odorless metabolite, trimethylamine N-oxide. Sometimes, a challenge test is performed where a patient consumes a choline-rich substance to assess the body’s ability to process the TMA precursor. Blood tests are also standard, used to check for nutritional deficiencies or to evaluate liver and kidney function.