Merck Manual

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Some Causes and Features of Diarrhea

Some Causes and Features of Diarrhea


Common Features*


Acute (less than 1 week)‡

Gastroenteritis Overview of Gastroenteritis Overview of Gastroenteritis due to viruses, bacteria, or parasites‡

Often vomiting

Rarely fever or blood in stool

Little or no abdominal pain (except during vomiting)

Sometimes recent contact with infected people (such as those at a day care center, at a camp, or on a cruise), with animals at a petting zoo (where Escherichia [E.] coli may be acquired), or with reptiles (where Salmonella bacteria may be acquired)

Sometimes recent consumption of undercooked, contaminated food or contaminated water

A doctor’s examination

Sometimes examination and testing of stool

Diarrhea that started suddenly, often with vomiting, within 4 to 8 hours of eating contaminated food

Often present in other people

Typically lasting 12 to 24 hours

A doctor’s examination alone

Side effects of drugs§ (including antibiotics, many cancer chemotherapy drugs, colchicine, and quinine/quinidine)

Recent use of a drug that causes diarrhea

Often no other symptoms

A doctor’s examination

Sometimes tests for Clostridioides difficile (formerly Clostridium difficile) toxin in stool

Chronic (4 weeks or more)

Dietary factors such as

  • Intolerance of cow’s milk

  • Overeating of certain fruits or juices (such as pear, apple, or prune)

Diarrhea only after consuming a substance that could cause diarrhea

Abdominal bloating and passing of gas (flatulence)

Explosive diarrhea

A doctor’s examination

Sometimes a breath test to detect hydrogen, indicating undigested food

Examination and analysis of stool to check for unabsorbed carbohydrates

Intermittent diarrhea associated with abdominal pain

Often diarrhea alternating with constipation

No bleeding, weight loss, or fever

Usually begins during the teens or 20s

Symptoms usually present for more than 12 weeks

Changes in the frequency of bowel movements or consistency of stool

A doctor’s examination

Sometimes blood tests and colonoscopy Endoscopy

Inflammatory bowel disease such as

Blood in stool, crampy abdominal pain, weight loss, and loss of appetite

Sometimes arthritis, rashes, sores in the mouth, and tears in the rectum



Stool tests

Malabsorption disorders such as

Light-colored, soft, bulky, and unusually foul-smelling stool that may appear oily

Abdominal bloating and flatulence

Weight loss

For tropical sprue, long-term (over 1 month) residence in a tropical country

For pancreatic insufficiency, usually in a person known to have a disorder of the pancreas (such as chronic pancreatitis Chronic Pancreatitis or cystic fibrosis Cystic Fibrosis (CF) )

Tests to measure the amount of fat in stool samples collected over several days

If celiac disease is suspected, blood tests to measure the antibodies produced when people with celiac disease eat foods containing gluten

For celiac disease and tropical sprue, especially celiac disease Celiac Disease Celiac Disease , biopsy of the small intestine

Certain tumors

For colon cancer, sometimes blood in stool, decreased stool diameter, and weight loss

For endocrine tumors, various symptoms, including abdominal pain or cramping, flushing, and massive watery diarrhea

Blood tests


Often nervousness, trouble tolerating a hot environment, fatigue, palpitations, weight loss, and rapid heart rate

Blood tests

Surgery on the stomach or intestines (such as gastric bypass for weight loss or removal of a significant length of intestine)

Obvious recent surgery

A doctor’s examination alone

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present.

† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made by the doctor's examination alone, without any testing.

‡ Diarrhea that has been present for 1 to 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea.

§ Certain infections and certain drugs can also cause chronic diarrhea.

CT = computed tomography; HIV = human immunodeficiency virus; MRI = magnetic resonance imaging.