Why Does Poop Smell Bad? The Science Behind the Unpleasant Odor of Stool

Regardless of the term used-poop, feces, or stool-there's no denying the unpleasant odor. The strong smell of excrement is inherent, arising from the byproducts of digestion.

Changes in stool odor could signal an underlying problem, as its makeup is affected by elements like diet, colon health, overall well-being, and the microbiome of the digestive system, consisting of microbes or bacteria present in the gut.

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Why Does Poop Smell Bad? The Science Behind the Unpleasant Odor of Stool

Decoding the Smell of Poop

The malodorous compound known as skatole, or 3-methylindole, contributes to the unpleasant smell of feces. This compound is produced by bacteria during the breakdown of the amino acid L-tryptophan in the gastrointestinal tract. Interestingly, in small concentrations, skatole imparts a pleasant scent to flowers like jasmine, according to the American Chemical Society.

The human body houses over 10,000 microbial species, with more bacterial cells than human cells, playing a crucial role in digestion and significantly impacting the odor of feces. The gases emitted during this process vary depending on the types of foods and substances broken down by different bacteria in the gastrointestinal tract and mouth.

Various factors, including dietary patterns, alcohol consumption, dietary supplements, and prescription medications, can influence the smell of feces, as bacteria break down ingested substances.

Sugar alcohols like sorbitol, found in candies, and sulfate-containing foods such as eggs, broccoli, cabbage, cauliflower, onions, legumes, and meat contribute to the production of sulfur gas, resulting in a rotten egg smell during digestion. Highly processed and sugary foods, challenging for bacteria to digest, can lead to increased gas production and a more unpleasant odor in feces.

Moreover, excessive alcohol intake can also contribute to smelly stools by disrupting intestinal function and the digestive process, according to Emma Laing.

If there is a noticeable change or worsening in stool smell, it is likely due to alterations in diet or medication, and the digestive process eventually adapts, with the intensified smell usually being temporary, according to Laing. Monitoring dietary choices and alcohol consumption can help individuals manage and understand changes in the odor of their stools.

Other Causes of Foul-Smelling Stool

The primary cause of foul-smelling stool is often related to one's diet, with factors such as specific foods or lactose intolerance playing a role. However, persistent bad odor, especially when accompanied by other symptoms may indicate an imbalance in the microbiome or an underlying disease like inflammatory bowel disease, warranting medical attention.

Here are five other reasons that could make a foul-smelling stool than the usual:

Irritable Bowel Syndrome- IBS is a chronic gastrointestinal disorder, that presents with symptoms like foul-smelling stool, abdominal pain, nausea, and changes in stool consistency. While there is no cure, treatments, including medications, help manage symptoms like belly pain and cramps.
Antibiotics- Loose and foul-smelling stools, occurring during and after antibiotic use due to changes in the gut microbiome, are typically temporary and not a major concern, with potential relief through probiotics or IBS-like medications.
Gastrointestinal Infection - GI caused by various factors like bacteria, viruses, or parasites, typically presents symptoms such as diarrhea or abdominal pain, and treatment depends on the identified cause, with antibiotics for bacterial infections, anti-parasitic medication for parasites, and supportive care for viral infections.
Inflammatory Bowel Disease- IBD involves inflammation of the digestive tract, with symptoms developing gradually or suddenly, and its causes include genetic factors and lifestyle choices.