Stool naturally has an offensive odor. This odor is a result of a combination of many factors. Stool is formed by a mixture of digested and undigested food material, water, secretions of gut (like enzymes, bile, and mucus), and intestinal flora (bacteria and fungi). During the passage of these substances through the gut (a process that might take a few hours to a few days), digestion, decomposition and fermentation of food occurs. The chemical and microbial processes of digestion also produce gas. The unpleasant odor of the stool is due to the combination of all these constituents of stool.
Any change in the composition of stool also causes a change in the odor of the stool. For example, changes in diet or intake of certain medicines causes a change in the usual odor of the stool. These changes are normal, and temporary. In these cases, the usual odor of stool usually returns after a few days.
In some cases, however, there is a foul odor in stools that is not a normal variation of stool odor. This may indicate an underlying pathological cause requiring medical attention. This is especially the case when the foul smelling stool is also accompanied by other signs and symptoms, such as nausea, vomiting, diarrhea, constipation, bloating, abdominal cramps or pain, and excessive belching and flatulence. A loss of appetite and an abnormal decrease in body weight may also accompany these signs and symptoms.
Abnormally Foul Odor of Feces
Apart from changes in the composition of daily diet, a foul stool odor may also be caused by changes in the normal microbial flora of the gut. This may happen as a result of infection by an external pathogen or an overgrowth of one of the normal resident bacteria in the intestine. Conditions resulting in insufficient digestion of food constituents and malabsorption of resulting nutrients could also promote foul odor in stools. Under these conditions, the normal microbial flora of the intestine decomposes a large amount of undigested food, resulting in formation of foul-smelling gases.
Causes of Bad Stool Odor
The following are some of the conditions associated with foul stool odors:
- Food poisoning: Food poisoning, mainly caused by bacterial toxins, causes irritation and inflammation of the gut. These pathogenic bacteria enter the digestive tract through consumption of contaminated food and water.
- Gastroenteritis: Gastroenteritis refers to inflammation of stomach and intestine, caused by a variety of pathogens (such as bacteria, viruses, and protozoa). Viral gastroenteritis is also known as stomach flu.
- Enterocolitis: Enterocolitis refers to inflammation of both small and large intestines. These are also caused by pathogens such as bacteria, protozoa, and viruses.
- Small intestinal bacterial overgrowth: Small intestinal bacterial overgrowth (also referred to as SIBO), is caused by an overgrowth of normal bacterial residents of the intestines. This overgrowth can be a result of anatomical abnormalities of the intestine, disorders of intestinal motility, and disturbances in the normal biological mechanisms that keep the growth of these microbes in check.
- Exocrine pancreatic insufficiency: Pancreatic enzymes are essential for proper digestion of food components. In conditions such as pancreatitis, the production and secretion of pancreatic enzymes is not sufficient for proper digestion to happen. Action of intestinal flora on the incompletely digested food can result in foul smelling stools.
- Food intolerance: Food intolerance is caused by the lack of proper enzymes to digest particular food components. Lactose intolerance is a common example of food intolerance that is associated with foul smelling stools caused by ingestion of milk and other dairy products.
- Irritable bowel syndrome: Irritable bowel syndrome (commonly referred to as IBS) changes gastrointestinal motility (making it too fast or too slow). It is also accompanied by muscle spasms of the bowel walls. In persons with IBS, foul-smelling stools are produced upon intake of certain foods.
- Inflammatory bowel disease: Inflammatory bowel disease is thought to be an autoimmune disorder that causes inflammation of bowels and other parts of the digestive tract.
- Short bowel syndrome: Short bowel syndrome is caused by the surgical removal of a part of the intestine. This interferes with proper digestion and absorption of food, because a short bowel has a reduced surface area compared to that of a normal length bowel.
- Celiac disease: Celiac disease is caused by immune sensitivity to gluten in food. In persons having celiac disease, intake of any foods containing gluten causes inflammation of the intestines.
- Bowel obstruction: Movement of stool through the intestines can slow down if there is any obstruction in the lumen of the intestine. Abnormal growths on the walls of the intestine (such as tumors or polyps) or a constriction of intestinal walls can cause bowel obstruction. Slow transit of undigested food through the intestine can cause smelly stools due to bacterial action.
- Gallbladder disease: Gall bladder secretions are important for proper digestion of food in the intestine. Therefore, gall bladder diseases can result in incomplete digestion of foods and smelly stools.
Diet and Lifestyle Remedies
Medical treatment is required in cases where the bad stool odor is caused by pathological conditions, such as microbial infections and other gastrointestinal disorders. A doctor will be able to provide the appropriate medical treatment after diagnosing the exact cause of the foul stool odor and other accompanying signs and symptoms.
There are also certain dietary and lifestyle changes that could be undertaken to manage the foul smell of stools. Some of these measures include:
- Avoiding certain foods: One can keep a daily food diary to investigate foods that produce a foul smell in the stool. Once identified, these offending foods could be removed or replaced in the daily diet.
- Reducing meal size: If digestion is a problem, then reducing meal size may help. This would enable optimal digestion and absorption, and reduce the amount of residual waste material on which bacteria can act to produce a foul smell.
- Increasing fiber intake: Insufficient fiber intake decreases the rate of movement of food through the gut. This can lead to foul smelling stools as the intestinal flora gets more time to decompose and ferment it. Increasing fiber intake in the diet helps build regular bowel habits, which reduce the transit time of digested food material through the intestine.
- Increasing water intake: Water constitutes about 60% of the mass of stools. Adequate water intake can reduce the chances of constipation and foul smelling stools.
Also read easy bowel movements.