Foul Smelling- Types, Causes, Diagnosis & Treatment

Stools are formed in the large intestine (colon) with the help of "good bacteria". These bacteria aid digestion, but changes in your diet or intestinal health can affect how your stool smells. Foul-smelling stool in children is often linked to food intolerance, infections, or malabsorption issues. If it persists, a medical evaluation is necessary.

Common Causes of Foul-Smelling Stool and Gas

Antibiotics and Infection

People taking antibiotics may experience temporary stomach pain, foul-smelling stools and gas because the drugs disrupt the gut's bacterial balance. This imbalance is one of the common smelly stool causes. Symptoms typically resolve after completing antibiotics and restoring healthy gut bacteria.

People who experience an overgrowth of harmful gut bacteria while taking antibiotics may notice the following signs:

• watery, foul-smelling stool with mucus or blood
• pain, tenderness, and cramps in the abdomen
• fever

These digestive changes are typical causes of smelly stools, especially when the gut flora is disturbed.

Lactose Intolerance

Lactose is a type of sugar found in milk and dairy products. The body uses lactase to digest it.

A person with lactose intolerance does not make enough lactase to digest lactose, leading to smelly stools and bloating.

People who are lactose intolerant may experience the following signs after consuming dairy products:

• Loose, foul-smelling stools
• Bloating and gas
• Abdominal cramps
• Nausea

This condition is one of the most common causes of foul-smelling stool.

Milk Allergy

Allergy Asthma and Immunology explains that milk allergy differs from lactose intolerance.

People who are allergic to milk have an immune reaction to milk and its products, sometimes producing smelly stools as part of the inflammatory response.

Signs of milk allergy include:

• Foul-smelling stool with blood
• Stomach ache
• Urticaria
• Rare severe reaction: anaphylaxis

Because digestion is disrupted, this can also fall under causes and remedies for bad stool smell, especially when inflammation is involved.

Short Bowel Syndrome

Short bowel syndrome (SBS) is a rare condition where part of the small or large intestine is missing or not functioning. This leads to malabsorption, a significant cause of smelly stools because nutrients are not properly digested. A common cause is the surgical removal of part of the intestine after treatment for inflammatory bowel disease (IBD).

Signs of SBS may include:

• Pale, oily, and foul-smelling stools
• Severe diarrhoea
• Dehydration
• Weight and muscle loss
• Lethargy
• Malnutrition
• Bloating
• Stomach pains

Malabsorption-related smelly stools often require long-term treatment and monitoring.

Chronic Pancreatitis

Chronic pancreatitis causes persistent inflammation and affects digestion, often leading to nutrient malabsorption and smelly stools.

Signs may include:

• Oily, greasy, and foul-smelling stools
• Nausea
• Vomiting
• Pain in the upper abdomen and back
• Pale or clay-coloured stools
• Malnutrition and weight loss
• Pale, oily, and foul-smelling stools
• Severe diarrhoea
• Dehydration
• Weight and muscle loss
• Lethargy
• Malnutrition
• Bloating
• Stomach pains

This condition is a major contributor to smelly stool causes, especially when fat digestion is impaired.

Conditions that Cause Foul-Smelling Stool

Foul-smelling stool can be a symptom of many digestive disorders and malabsorption issues. These are among the well-known causes of foul-smelling stool and causes of smelly stools:

• Ulcerative Colitis
• Cystic Fibrosis
• Giardiasis (Parasitic Infection)
• Tropical Sprue
• Bile Acid Malabsorption
• Intestinal Ischemia
• Colon Cancer
• Whipple's Disease
• Bacterial Overgrowth Syndrome (SIBO)
• Liver Disease
• Gallbladder Disease
• Steatorrhea due to Fat Malabsorption

Some of these conditions also contribute to abdominal swelling and smelly stools, especially when inflammation or infection is involved.

Related Symptoms

Common accompanying symptoms include:

• Diarrhoea or loose stools
• Bloating and gas
• Nausea or vomiting
• Abdominal cramps or pain
• Pale or oily stools
• Fatigue or lethargy
• Weight loss or malnutrition
• Fever (in infections)
• Blood or mucus in stool

These symptoms often appear alongside smelly stools depending on the underlying digestive condition.

When to See a Doctor?

Visit a gastroenterologist if you experience any of the following:

• Black or pale stools often
• Blood in the stool
• Changes in the stool related to diet
• Chills
• Cramping
• Fever
• Pain in the abdomen
• Weight loss

Early diagnosis helps in finding the exact smelly stool causes and selecting the right treatment for smelly stools, especially when infections, malabsorption, or chronic digestive disorders are present.

Diagnosis and Tests

Antibiotics and infection

In most cases, a doctor can diagnose stomach pain associated with antibiotics by doing a physical exam and asking about a person's history of antibiotic treatment. They may also request a stool sample to check for bacterial toxins.

Lactose intolerance

People who suspect they are lactose intolerant should eliminate all dairy products from their diet for several days. After the dairy-free period, they should reintroduce milk or dairy products to see if the symptoms return.

Other diagnostic tests include:

• Blood test: This shows whether or not a person can successfully digest lactose after consuming products that contain it.
• A hydrogen breath test involves repeatedly blowing into a bag after consuming lactose. If the collected air contains high levels of hydrogen, this indicates lactose intolerance.
• A stool acidity test is a test of a person's stool after ingesting lactose. A very acidic stool sample suggests lactose intolerance.
• A genetic test involves analysing a blood or saliva sample for a gene linked to lactose intolerance.
• Surgical biopsy of the intestine: A surgeon removes a small piece of the intestine for analysis.

Milk allergy

According to the ACCAI, diagnostic tests include:

• Skin test: A doctor dabs some milk on the person's arm, then lightly pricks the area with a needle. Irritation at the site indicates an allergy.
• Blood test: This checks for antibodies to immunoglobulin E, which the body produces in response to allergens.
• Real food challenge: A person consumes a small amount of the allergen in the presence of a doctor or allergist.

Short bowel syndrome

A doctor may order the following tests to help diagnose SBS:

• Blood tests: These can check for anaemia, malnutrition, and dehydration.
• Imaging techniques (abdominal X-rays and CT scans): Check for obstructions and loss of bowel function.
• Liver biopsy: This can check liver function.

Chronic pancreatitis

A doctor will do a physical exam and take a thorough medical history. They may also order the following diagnostic tests:

• CT scan
• Magnetic resonance cholangiopancreatography, a type of MRI scan that uses a dye to make it easier to see internal organs
• Abdominal ultrasound
• Endoscopic ultrasound, in which a doctor inserts a flexible tube, or endoscope, into the small intestine through the mouth

Treatment and Management

Antibiotics and Infection

Usually, symptoms of foul smell go away soon after a person finishes antibiotic treatment. In the meantime, the following home treatments may help reduce the severity of symptoms:

• Drink lots of fluids.
• Avoiding wheat, dairy, and foods high in fibre, which can further irritate the intestines

Milk Allergy

• The only way to manage a milk allergy is to avoid milk and products containing milk.
• The ACCAI also notes that a doctor or allergist may advise someone with a milk allergy to carry an epinephrine pen.
• These allow a person to self-inject epinephrine in the event of anaphylactic shock.

Short Bowel Syndrome

Doctors usually tailor treatment for SBS to a person's symptoms and the amount of bowel they affect. Some treatment options include:

• Anti-diarrheal drugs
• Medicines to replace the intestinal lining
• Dietary adjustments
• Intravenous fluids
• Surgery

Chronic Pancreatitis

According to the National Pancreas Foundation, treatments for chronic pancreatitis focus on pain relief. They may include:

• Take pain relievers: Undergoing a whipple procedure or surgery to remove pancreatic lesions, having a pancreatectomy or surgery to remove all or part of the pancreas.

How to Prevent Foul-Smelling Stool?

Here are some ways to prevent foul-smelling stools:

Make dietary changes

Dietary changes can help prevent foul-smelling stools. For example, avoid drinking raw or unpasteurized milk. If you have a condition that affects how you absorb food or how your body responds to certain foods, your doctor can create the proper diet for you.

Following this diet plan can help reduce symptoms such as:

• Abdominal pain
• Abdominal bloating
• Foul-smelling stool

For inflammatory bowel disease (IBD), you can follow a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs).

Handle Food Correctly

Avoid bacterial infections in your food by handling it properly. Cook raw foods well before eating them. Examples include:

• Beef
• Poultry
• Pork
• Eggs
• Cooking well means checking the internal temperature of your food with a thermometer before you eat it.
• Check with your local health department for the minimum internal temperature each type of food should reach before eating it.
• Do not prepare meat and vegetables on the same cutting board. Preparing them on the same board can spread Salmonella or other bacteria.
• You should also wash your hands thoroughly after handling raw meat or using the toilet.

Home Remedies For Foul-Smelling Stool

• Hydration: Drink plenty of water to prevent dehydration.
• Probiotics: Help restore gut flora after antibiotic use.
• Ginger or peppermint tea: May soothe the stomach.
• BRAT diet: Bananas, rice, applesauce, and toast can help firm stools.

Lifestyle Changes for Managing Foul-Smelling Stool

• Maintain a balanced, low-fat diet.
• Avoid trigger foods (e.g., dairy if lactose intolerant).
• Eat smaller, frequent meals to ease digestion.
• Engage in regular physical activity.
• Manage stress to reduce gastrointestinal symptoms.