10 Possible Causes of Sudden or Chronic Diarrhea

Uncovering the Underlying Reason You Have Diarrhea

Diarrhea is a common problem that usually is a symptom of an underlying condition. There are many possible causes of diarrhea, including infections, food allergies or intolerances, and even medication. Therefore, it can take some work by you and your doctor to identify the underlying condition that's causing your diarrhea.

When exploring the various possible causes for your problem, you'll need to determine whether your diarrhea came on suddenly or gradually, and whether it might be related to foods you're eating. Chronic diarrhea is diarrhea that has persisted for weeks or even months.

Here's a primer on the various causes of diarrhea, both sudden and chronic, the additional symptoms you can expect with it, and possible treatments for the problem.

causes of diarrhea
Illustration by Brianna Gilmartin, Verywell 

Causes of Sudden (Acute) Diarrhea

"Acute diarrhea" starts, well, suddenly. It often brings with it other symptoms, such as nausea, vomiting, headache, and fever.

The most common cause of diarrhea, especially diarrhea that starts suddenly, is an infection—this can mean an infection from bacteria, a virus, or a parasite. There are many possible causes of acute diarrhea, but the three most common are:

1) Food Poisoning

Food poisoning occurs when you eat food that is contaminated with bacteria. The bacteria build up toxins in the food that make you sick. Causes of food poisoning are poor sanitation or food being stored at the wrong temperature.

  • How long diarrhea lasts: Usually less than two days
  • Triggered by: Toxins in food
  • Symptoms appear within: Two to six hours of ingesting the food
  • Appearance: Explosive, watery
  • Other symptoms: Abdominal cramps, fever, vomiting, weakness

2) Traveler’s Diarrhea

Traveler’s diarrhea is caused by eating food or drinking water that is contaminated with bacteria or parasites. Most traveler’s diarrhea will get better with home care in a few days. If you have recently traveled to a tropical country and you have diarrhea, call your doctor.

  • How long diarrhea lasts: Usually less than one week
  • Triggered by: Food or water that is contaminated by bacteria, viruses, or parasites
  • Symptoms appear within: 12 to 24 hours
  • Appearance: Explosive, watery, sometimes contains mucous or blood
  • Other symptoms: Possibly vomiting and/or fever

3) Stomach Flu

When stomach flu, also known as gastroenteritis, is caused by a virus, it's not the same that causes seasonal flu. An example of a virus that can cause stomach flu is rotavirus. Gastroenteritis also can be caused by a bacterium or a parasite. You can generally care for your stomach flu with home treatment. Young children, the elderly, and people with compromised immune systems are at risk for dehydration, and should be watched closely for signs of more serious complications.

  • How long diarrhea lasts: Usually three to eight days
  • Triggered by: A virus, bacterium, or parasite
  • Symptoms appear within: two days after exposure
  • Appearance: Watery
  • Other symptoms: Vomiting, fever, achiness

Causes of Chronic Diarrhea

Diarrhea that goes on for weeks or months may be caused by an infection, or it may be caused by an underlying medical condition. Here are some of the possible causes of chronic diarrhea and there are many more.

If you have had diarrhea for more than three days, seek help from your doctor.

4) Celiac Disease

If you have untreated celiac disease, you may have a hard time linking your symptoms with a specific food because your gut is damaged and you may experience symptoms all the time.

  • How long diarrhea lasts: More than four weeks
  • Triggered by: Gluten, but may hard to pinpoint your symptoms to a specific meal
  • Appearance: Large, bad-smelling stools that float in water and may appear greasy
  • Other symptoms: Unintended weight loss, lack of energy, lack of growth in children, plus many other possible symptoms

5) Food Allergy

Symptoms of classic Ig-E mediated food allergy begin within minutes to hours of eating a trigger food. It is possible to be allergic to any food, but a few foods cause the most common food allergies.

  • How long diarrhea lasts: Usually less than 24 hours
  • Triggered by: A specific food
  • Symptoms appear within: Two hours
  • Appearance: Watery, may contain blood
  • Other symptoms: Hives; vomiting; swelling of face, tongue or throat; eczema

6) Food Intolerance

Food intolerance is caused by a lack of the enzymes needed to digest a specific food. Lactose intolerance, the inability to digest the sugars in milk, is the most common, but it's possible to be intolerant of other foods as well.

  • How long diarrhea lasts: More than four weeks
  • Triggered by: A specific food
  • Symptoms appear within: two to 12 hours
  • Appearance: Watery, sometimes contains mucous
  • Other symptoms: Gassiness, abdominal cramps or pain

7) Inflammatory Bowel Disease

Inflammatory bowel disease includes Crohn's disease and ulcerative colitis, both of which have chronic diarrhea as a symptom. Both are incurable chronic diseases of the digestive tract that may be treated with surgery or managed with medication.

  • How long diarrhea lasts: More than four weeks
  • Triggered by: Not related to a specific food
  • Appearance: Blood or mucous in stool
  • Other symptoms: Abdominal pain, fever, weight loss, delayed growth in children

8) Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) describes chronic diarrhea, constipation, and abdominal pain that does not have a known disease as a cause. If you have been diagnosed with IBS, discuss the possibility of celiac disease with your doctor. The American College of Gastroenterology recommends that anyone diagnosed with IBS and diarrhea be tested for celiac disease.

  • How long diarrhea lasts: At least six months
  • Triggered by: Not related to a specific food, though certain foods may aggravate symptoms
  • Appearance: Small, frequent stools
  • Other symptoms: Chronic abdominal bloating or distention, constipation. Pain is relieved by bowel movement

9) Milk/Soy Protein Intolerance

Infants usually show signs of protein intolerance within a few months of birth. Some infants may react to food proteins present in breastmilk while others may react to formulas based on either cow’s milk or soy.

  • How long diarrhea lasts: More than two weeks
  • Triggered by: Dairy or soy products, sometimes by egg or other proteins
  • Symptoms appear within: two hours or more
  • Appearance: Streaks of mucous or blood
  • Other symptoms: Distended belly, crying, failure to thrive

10) Medication

Some medications, in particular antibiotics and chemotherapy, can cause diarrhea. You may have a reaction to the medication itself or an additive, such as a flavoring. The medication can also alter the balance of bacteria in your gut, causing abdominal pain and diarrhea. Talk to your doctor if you have diarrhea after starting a new medication.

When to See the Doctor

You can care for most diarrhea using at-home treatments, but some symptoms need immediate medical care.

If you experience sudden diarrhea that lasts for longer than around 48 hours, you should seek medical treatment at your doctor's office or at an urgent care clinic.

Dehydration can become a problem. If there's blood in your diarrhea, you should seek medical assistance immediately, regardless of how long you've had it. Meanwhile, if you've been experiencing chronic diarrhea, you should talk to your doctor about symptoms and whether testing is needed to determine the cause.

What Your Doctor Will Ask About Your Diarrhea

In order to figure out the cause of your diarrhea, your doctor is likely to ask you these questions:

  • How long have you had diarrhea? While not an absolute rule, diarrhea that started suddenly in the last 24 hours may indicate an infection or virus. If it has been going on for months or years, you may have a food intolerance or inflammatory bowel disease.
  • When did it begin? You doctor will want to know if you were traveling out of the country recently or if you ate any foods you suspect are causing your diarrhea. Food allergy symptoms begin immediately after eating a food, while diarrhea caused by intolerances or infections may be delayed by 12 hours or more.
  • How many stools a day are you having? Healthy people can have as many as two to three stools per day and as few as two to three stools per week. Three or more unformed stools a day is the cutoff for diarrhea.
  • What does it look like? Diarrhea may be loose stools, watery, mucous-y, or dark-colored. Black or bright red diarrhea may mean there is blood in your stool, which is a serious condition that needs immediate medical care.

A Word From Verywell

Diarrhea may be an inconvenience that is soon gone, or it can be a serious or long-lasting illness. When you have a bout, be sure you are drinking enough fluids and see your doctor if it persists.

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