A persistent and unexplained odor resembling sewer gas is often caused by the body’s production and subsequent excretion of volatile sulfur compounds (VSCs). The primary compound responsible is hydrogen sulfide (H2S), a gas recognized by its potent rotten egg or sewage-like scent. While low levels of H2S are normal byproducts of metabolism, an excessive amount usually signals an underlying physiological imbalance. Understanding the source of VSCs is the first step toward finding a solution.
Digestive System Origins
The most frequent source of excessive hydrogen sulfide (H2S) is the gastrointestinal tract, specifically the activity of anaerobic bacteria. These microorganisms produce H2S as a metabolic waste product when breaking down sulfur-containing molecules in food. Foods rich in sulfur, such as certain proteins and cruciferous vegetables like broccoli and cauliflower, provide the necessary substrate for this process. This bacterial action is a normal part of digestion, but an overgrowth or imbalance can lead to symptom development.
A common condition linked to this problem is Small Intestinal Bacterial Overgrowth (SIBO), particularly the hydrogen sulfide-dominant subtype. In SIBO, bacteria from the large intestine colonize the small intestine, where they ferment carbohydrates and sulfur-rich compounds prematurely. This fermentation generates large volumes of H2S gas, which can cause significant bloating and sulfurous flatulence.
The gas is absorbed into the bloodstream, circulating throughout the body before being released via the breath and sweat. Issues with gut motility, such as chronic constipation, can also contribute to this odor. Stagnation allows bacteria extended time to ferment and produce VSCs, further increasing the systemic load of the foul-smelling gas.
Systemic Metabolic Explanations
In some cases, the body’s inability to properly process sulfur compounds, rather than just overproduction in the gut, is the main driver of the systemic odor. The liver and kidneys are the primary organs responsible for metabolizing and filtering these compounds, including sulfur-containing amino acids like methionine and cysteine. When the enzymes responsible for these processing pathways are deficient or impaired, the sulfur-based compounds build up in the body.
This systemic accumulation forces the body to excrete the unmetabolized substances through alternative routes, primarily the breath, sweat, and urine. While rare genetic conditions exist that impair the metabolism of sulfur compounds, acquired issues like liver or kidney dysfunction can also reduce the body’s filtering capacity. When these organs cannot adequately neutralize or eliminate waste products, these odorous molecules are circulated and then released through the skin and lungs, resulting in a pervasive, full-body odor.
Localized Causes and Contributing Factors
Beyond systemic and intestinal issues, the sewer-like smell can originate from localized areas, most notably the mouth. Severe halitosis, or bad breath, is frequently caused by bacteria on the back of the tongue or deep within the gums and tonsils. These bacteria break down proteins and cellular debris, producing VSCs, including hydrogen sulfide, which manifests as a persistent, foul odor. Conditions like advanced periodontal disease or the presence of tonsil stones are common localized culprits.
The skin itself can also be a source of localized, sulfurous smells due to certain infections or high concentrations of odor-producing bacteria. Bromhidrosis, a condition involving abnormal body odor, occurs when skin bacteria break down sweat components, sometimes resulting in a sulfur-like or onion-like scent. Various medications can also alter the chemical composition of sweat, leading to the excretion of sulfur-containing metabolites through the skin.
When to Seek Medical Attention and Diagnostic Steps
If a persistent, unexplained sewer odor is present, it warrants consultation with a healthcare provider, such as a primary care physician who may then refer to a gastroenterologist or dermatologist. A sudden onset of the odor, especially when accompanied by other symptoms like chronic diarrhea, abdominal pain, or unexplained weight loss, requires prompt medical evaluation. The diagnostic process typically begins with a thorough medical history and physical examination.
For suspected digestive causes, a specialized breath test is a common, non-invasive diagnostic tool for SIBO. This test measures the gases produced by bacteria in the small intestine, including the specific hydrogen sulfide gas. In cases where a metabolic disorder is suspected, blood and urine tests are used to measure levels of certain metabolites, which can indicate an enzyme deficiency or organ dysfunction. A dental examination is also often performed to rule out localized oral causes.