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8 Causes of Diarrhea

Loose or watery stool is very common, but there are ways to treat it.
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Written by
Adam Pont, MD, PhD.
Gastroenterology Fellow, New York Presbyterian Hospital/Columbia
Last updated March 17, 2021

Diarrhea questionnaire

Answer our clinicians' questions to get a diarrhea treatment prescription for $25 and know if your diarrhea is serious.

Diarrhea questionnaire

Answer our clinicians' questions to get a diarrhea treatment prescription for $25 and know if your diarrhea is serious.

See diarrhea treatment options

Only available in: CA, NY, TX, FL, IL, NC, PA, OH, MI, and WA

What’s causing your diarrhea?

Bowel movements are considered diarrhea when you have very loose or watery stool or if you have loose stool three or more times within a day. While there are many causes of diarrhea, what’s usually happening is more fluid is going through your intestines than can be reabsorbed.

Common causes of acute (or short-term) diarrhea include a viral infection (“stomach flu”), bacterial infection (including C. Difficile colitis), or medication side effects.

Common causes of chronic diarrhea include irritable bowel syndrome, inflammatory bowel disease (ulcerative colitis and Crohn’s disease), and celiac disease.

Depending on the cause, you may have other symptoms including nausea, vomiting, abdominal pain, fatigue, or fever.

If you have diarrhea, it is important to drink plenty of fluids to replace the excess water being lost in the loose stools. You may need to drink a rehydration drink like Gatorade, which contains electrolytes. You can also take anti-diarrheal medications in some cases.

Causes

1. Viral gastroenteritis

Symptoms

Viral gastroenteritis (also known as “stomach flu”) is a very contagious and common illness that affects both children and adults.

It is caused by viruses like norovirus and rotavirus. You catch it by eating contaminated food or drinks (“food poisoning”), by touching contaminated surfaces, or by coming into contact with an infected person’s vomit or stool.

Outbreaks are common in confined settings with many people, like cruise ships, nursing homes, or childcare centers. Symptoms usually come on quickly and last for a few days. You are usually contagious for a while even after symptoms go away.

The main treatment is to drink plenty of fluids, like water or a special oral rehydration solution. It can become serious if you get severely dehydrated.

You can also take over-the-counter anti-diarrheal medications (unless you also have a fever), but do not take more than the recommended dose. Since it is caused by a virus, antibiotics are not helpful.

2. Bacterial infection

Symptoms

  • Diarrhea (may be bloody)
  • Abdominal pain
  • Nausea and vomiting
  • Fever

Many different bacteria can infect your intestines and cause diarrhea. Sometimes bacteria in contaminated food or water also make toxins that cause diarrhea. You can get it up from eating improperly prepared or contaminated foods (“food poisoning”) or from contaminated water (if you travel to areas with poor sanitation).

Symptoms usually begin within hours to a couple days after consuming the bacteria or toxins. They can last for several days or longer. Fever and bloody diarrhea can occur. It can become serious if you get severely dehydrated.

The main treatment is to drink plenty of fluids, preferably water or a special oral rehydration drink. If your diarrhea continues for several days, your doctor may prescribe antibiotics. You can use over-the-counter anti-diarrheal medications (unless you have bloody diarrhea or fever). Be sure not to take more than the recommended dose.

3. C. Difficile colitis

Symptoms

  • Frequent and a lot of watery diarrhea
  • Fever
  • Abdominal pain
  • May also have nausea or loss of appetite

C. Difficile colitis is a severe inflammation of the colon (colitis) caused by C. Difficile (C. Diff) bacteria. It primarily affects people in hospitals or nursing homes, but C. Diff is now being caught outside those settings. It is very contagious.

The infection often occurs after people take antibiotics. The antibiotics change the “good” bacteria in your gut, allowing the C. Diff to gain a foothold and cause an infection.

Other people at risk include the elderly, people with weakened immune systems or other intestinal diseases (such as ulcerative colitis or Crohn’s disease), or who have had C. Diff before.

The infection is diagnosed by testing a sample of your stool.

If you are diagnosed with C. Diff colitis, your doctor will prescribe a course of gut-specific antibiotics. Your symptoms should improve within several days, but be sure to finish all of the antibiotics. If you don’t finish, you are at high risk of the infection coming back.

You should also drink plenty of fluids, like water or a special oral rehydration solution. Do not take over-the-counter anti-diarrheal medications unless your doctor advises you to.

Dr. Rx

For C. Diff infection, it really can happen after just one dose of antibiotics. I have had multiple patients who had one dose of antibiotics for a procedure or other indication, and then several weeks to months later had diarrhea ultimately found to be C. Diff related. This is one of many reasons that doctors only prescribe antibiotics when they are absolutely needed. —Dr. Adam Pont

Diarrhea questionnaire

Answer our clinicians' questions to get a diarrhea treatment prescription for $25 and know if your diarrhea is serious.

See diarrhea treatment options

Only available in: CA, NY, TX, FL, IL, NC, PA, OH, MI, and WA

4. Medications

Symptoms

  • Non-bloody diarrhea

Certain medications can cause diarrhea. Laxative medications may cause diarrhea when taken in excess or are abused (extreme use). Many other medications may cause diarrhea as a side effect, including most antibiotics, some antacids that contain magnesium, many chemotherapy drugs, some antidepressants (SSRIs), and metformin (a diabetes medication). Some herbal supplements may also cause diarrhea.

You may need to change your medication dose or timing, or switch to a different medication. In some cases, the diarrhea may improve with time even if you keep taking the medication. You should always speak with your doctor if you have a medication side effect. Do not stop taking a prescribed medication before talking to your doctor.

5. Irritable bowel syndrome

Symptoms

  • Belly pain more than once a week, often related to bowel movements
  • Diarrhea
  • Stool becomes frequent (more than 3 times a day)

Irritable bowel syndrome (IBS) is a chronic disorder of the gut (primarily the large intestine) that causes abdominal pain and changes in bowel movements. In diarrhea predominant IBS (IBS-D), diarrhea is the main bowel symptom. You may have more frequent bowel movements (more than three daily). You may feel sudden urges to have bowel movements, causing you to rush to the toilet. You might feel bloated or gassy.

IBS is more common in women, people under 50, and people with mental health issues (particularly depression and anxiety.)

IBS is a chronic disease, meaning that symptoms last for months or years (although the symptoms usually come and go over time). Stress often worsens symptoms.

Treatment can involve several approaches. You may need to change your diet if any foods or drinks trigger your symptoms. Your doctor may recommend fiber supplements, regular exercise, and ways to manage life stressors (including getting enough sleep). There are also several prescription medications that can help with your symptoms.

Pro Tip

The events surrounding when your diarrhea started are very important to help diagnose the cause. Any new foods, restaurant meals, sick contacts, travel, medication changes, should be mentioned to your doctor. —Dr. Pont

6. Celiac disease

Symptoms

Celiac disease is a chronic inflammatory disease caused by a reaction to eating gluten (a protein in wheat, rye, and barley). In people with celiac, gluten causes your immune system to attack the lining of your small intestines. The damage to your small intestine can interfere with your ability to absorb nutrients, so you may get iron deficiency anemia or low bone density. You may also have fatigue or an itchy rash.

To diagnose celiac disease, you’ll have a combination of blood tests and an upper endoscopy (the doctor places a tube with a camera down your throat to view your digestive tract). It is important that you do not stop eating gluten before getting tested—it can lead to false negative results.

The treatment for celiac is to completely avoid gluten and food with gluten in it. You may also need vitamin or mineral supplements if you have nutritional deficiencies.

7. Ulcerative colitis

Symptoms

  • Crampy abdominal pain
  • Frequent bloody diarrhea—may wake you up at night
  • Urgent need to have bowel movements, often with very little warning
  • Feeling that you still need to pass stool, even when nothing is coming out
  • Fever
  • Weight loss

Ulcerative colitis (UC) is a type of inflammatory bowel disease (IBD) caused by abnormal immune system activity primarily in your large intestine. It is a chronic disease that develops over time with bouts of severe symptoms, or “flares.”

UC causes inflammation in the lining of the large intestine, leading to ulcers and bleeding along with other symptoms. The last part of your large intestine (rectum) is always affected and parts of your intestine further up can be affected as well.

Diagnosis is usually done by performing a colonoscopy and taking small biopsy samples of the intestinal wall. UC increases your risk for colon cancer. It is important that you are treated by a specialist in digestive diseases (a gastroenterologist).

There are many options for treating UC, including pills and medications that are injected (through an IV or under your skin). Although there is no cure, the goal of treatment is to put it in “remission.” That’s when you have no symptoms, allowing the intestine lining to heal. If medications are not successful, you may require surgery to remove your large intestine.

8. Crohn’s disease

Symptoms

  • Abdominal pain. Tends to be in the right lower part of the abdomen, but it can be anywhere. Often cramping-type pain.
  • Fever
  • Weight loss
  • Diarrhea
  • Palpable (can feel with your hand) mass in your abdomen
  • Severe nausea and vomiting (if there’s an intestinal blockage from severe inflammation)

Crohn’s disease is a type of inflammatory bowel disease (IBD). It's caused by abnormal immune system activity. You will usually have inflammation in the area of your gut where the small intestine meets the large intestine. But any part of your digestive tract from your mouth to your anus can be affected.

It is a chronic disease causing episodes of intense symptoms, called “flares.” You’ll be referred to a gastroenterologist to be diagnosed. The doctor will do an endoscopy or colonoscopy (or both), along with other imaging, like a CT or MRI scan.

There are many treatments for Crohn’s including pills or medications that are injected (through an IV or into the skin.) Sometimes a medication will become less effective, and you will need to switch to another medication.

Just under half of all people with Crohn’s will need surgery within 10 years of their diagnosis. Sometimes, a less invasive procedure can be done instead. There is no cure for Crohn’s, but most people will see significant improvement in symptoms with treatment.

Diarrhea questionnaire

Answer our clinicians' questions to get a diarrhea treatment prescription for $25 and know if your diarrhea is serious.

See diarrhea treatment options

Only available in: CA, NY, TX, FL, IL, NC, PA, OH, MI, and WA

Other possible causes

Many other less common conditions may cause diarrhea, including food allergies or intolerances, parasites, malabsorption, microscopic colitis, radiation exposure (often from treatment of abdominal or pelvic cancers), endocrine disorders, and colon cancer or other tumors.

When to call the doctor

Diarrhea will usually begin to improve within 3 days. If your symptoms last longer than 3 days with no improvement (or your symptoms worsen), you should contact your primary care doctor.

However, do not wait to call your doctor for diarrhea symptoms if:

  • You have diarrhea that is bloody
  • You have a persistent fever (temperature over 100.4 F)
  • You are elderly or are immunocompromised
  • You are pregnant
  • You are taking or have just finished taking a course of antibiotics

Pro Tip

Ask your doctor: How long will my diarrhea last? It’s also worth asking in finer detail—will my diarrhea first become less common, and then disappear? This will help you have realistic expectations for recovery and know better when to contact the doctor for follow up if needed. —Dr. Pont

Should I go to the ER for diarrhea?

Go to the ER if you have these symptoms:

  • Your stool is mostly bright red blood or dark, black tarry liquid (with very little formed stool, and not just a few drops of blood).
  • You are unable to keep down any liquids or food without immediately vomiting.
  • You have signs of severe dehydration: decreased urine output, very dark urine, confusion, or new lightheadedness (especially when sitting up or standing).
  • Your diarrhea suddenly stops and you become constipated, particularly if you also have fever or worsening abdominal pain. This could be a sign of a medical emergency requiring prompt medical intervention.

At-home diarrhea treatments

Most diarrhea will begin to improve after 3 days. Until your symptoms go away, it is important to:

  • Drink plenty of water and oral rehydration solutions. If mostly drinking water, you should also eat more sodium (salt) than usual (for instance, salty pretzels or crackers).
  • Continue to eat whatever food that you can tolerate. Unless you think a certain food is causing your diarrhea, there is no need to restrict your diet
  • Over-the-counter anti-diarrheal medications like loperamide or bismuth subsalicylate may help with new diarrhea symptoms. They are less effective (and possibly dangerous) for chronic causes of diarrhea. It is very important to use loperamide only as directed and to not exceed the recommended doses. Bismuth may turn your stool black temporarily. Do not use these medications if you have a fever, bloody diarrhea, or C. Diff.
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Gastroenterology Fellow, New York Presbyterian Hospital/Columbia
Dr. Pont is currently a fellow in Gastroenterology at New York Presbyterian Hospital/Columbia, where he also completed his residency in Internal Medicine. Dr. Pont received his medical degree and PhD at the New York University School of Medicine. He earned his BS in Biological Systems Engineering at the University of Nebraska-Lincoln.

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