Diarrhea is a very common digestive disorder that all of us have experienced more or less frequently.  It can be caused by a multitude of health conditions, and even stress and anxiety. Most of the time, it is caused by food intolerance or bacterial infection. However, it can also be the symptom of a more serious condition. If you have diarrhea and can not pinpoint the reason behind it, please read on.

What Is Diarrhea Anyway?

Diarrhea is a transit disorder characterized by loose or even watery stools in abnormally large quantities or with an increased frequency of occurrence, of the order of several times a day.

Diarrhea can be occasional, lasting less than 2 weeks, in which we speak of acute diarrhea, or chronic when it lasts for more than a month. Diarrhea is not a disease in itself but a symptom of another pathology and can be found as a symptom of a large number of conditions.

Diarrhea is often accompanied by nausea, vomiting, abdominal pain, cramps, or fever depending on the underlying cause.

Most Common Causes of Diarrhea

A bacterial Infection

Dysenteric diarrhea is manifested by the discharge of mucus and blood (sometimes without feces) with abdominal pain, vomiting, and sometimes fever. There may also be joint or skin signs.

Dysenteric diarrhea is caused by bacteria that invade the intestinal wall like Salmonella, Shigella, Campylobacter, or bacteria that produce toxins like enterotoxigenic Escherichia coli.

Sometimes a parasite (amebiasis) can be involved. In some countries, amebiasis can also cause diarrhea, and Escherichia coli or Shigella Dysenteriae can cause what is called traveler’s or tourist’s diarrhea.

Pastries, minced beef, pork, ready meals, shellfish, raw dairy products, etc. are also responsible for food poisoning with diarrhea. The bacteria involved are then Staphylococcus Aureus, Salmonella, Yersinia Enterocolitica.


Taking antibiotics causes a change in intestinal transit in about 1 in 5 patients. This drug-induced diarrhea starts during treatment but can also last for two months after stopping.

Nonsteroidal anti-inflammatory drugs, colchicine, and certain cancer chemotherapy drugs are also responsible for drug-induced diarrhea.


This is the biggest threat associated with diarrhea. During an episode of diarrhea, watery stools, vomiting, sweating, urine, and respiration cause water loss and leakage of electrolytes (sodium, chloride, potassium, and bicarbonate). Dehydration occurs when these losses are not compensated for. Conversely, dehydration can also lead to diarrhea.

Food Poisoning

Food poisoning can also be the cause of your diarrhea. Indeed, symptoms of food poisoning include nausea, vomiting, and diarrhea, which are the body’s defense mechanisms to evacuate the pathogen. To this can be added fever and headaches.

Anxiety & Stress

When you are nervous, stressed, or anxious, your digestion is also disturbed. Your body produces chemicals that affect the nervous system, which in turn speeds up digestion. This disrupts the natural balance of your digestive system; your body then absorbs less fluids than usual and your bowel movements become more frequent and watery as a result. The stress then causes a transient diarrhea attack.

Lactose Intolerance

Lactose intolerance is an abdominal syndrome marked by the appearance of stomach ache, acute abdominal pain, bloating and diarrhea, sometimes vomiting especially in children, 30 minutes to 2 hours after ingestion of dairy products, due to due to their high lactose content.

If you have diarrhea every time after consuming dairy products, that might be the cause.

Chronic Pancreatitis

Chronic pancreatitis usually causes upper abdominal pain, with radiation to the back, nausea, weight loss, and/or jaundice, leading to malabsorption of food, with signs of weight loss and loose stools and/or diarrhea.

Pancreatic Cancer

If you suffer from pancreatic cancer, you will also experience diarrhea. Indeed, the symptoms of pancreatic cancer include digestive complaints (such as loss of appetite, unexplained weight loss, flatulence, fatty stools, and diarrhea) often in combination with a feeling of pressure in the upper abdomen and possibly a newly discovered diabetes mellitus as a so-called first symptom (especially in younger patients).


Gastrinoma is a tumor of the pancreas that makes large amounts of the hormone gastrin. It stimulates the stomach to secrete acid. The overproduction of gastrin can lead to gastrointestinal ulcers and cause diarrhea, severe abdominal pain, and internal bleeding.

Cystic Fibrosis

Severe pain within minutes of eating food and diarrhea without blood or mucus is the most commonly reported symptoms of cystic fibrosis, with almost all patients experiencing these symptoms at some point during the illness.

Fructose Intolerance

With fructose intolerance, the patient’s body is incapable of transporting fructose from the small intestine to the blood. So, like with lactose intolerance, fructose ends up in the large intestine and serves as food for the bacteria there. This results in the production of gases, such as carbon dioxide and methane, as well as fatty acids. More water is also “carried away” in the intestine as the fructose breaks down, causing diarrhea.

Celiac Disease (Gluten Intolerance)

Celiac disease or gluten intolerance is the most common cause of another mechanism of chronic diarrhea: malabsorption diarrhea. Nutrients are insufficiently absorbed in the small intestine. The stools are then more abundant.

Food Allergy and Intolerance

Digestive issues such as nausea, diarrhea, and stomach discomfort can be caused by food intolerance and allergies. Your immune system perceives some foods as a threat to your body and reacts in the form of an allergy to get rid of the “unwanted” elements. Diarrhea is one of the quickest and most efficient ways to rid the body of unwanted foods.

Chronic Inflammatory Bowel Disease

IBD is characterized by diarrhea, which is the most frequent symptom. Indeed, the illness can influence transit time, making it faster and allowing for less water absorption. This results in watery stools.

Crohn’s disease, an inflammatory bowel illness, can damage the small intestine, preventing normal food absorption and leading to diarrhea and increased fat and nutrient excretion.

Last Words

There are, of course, other conditions that can cause diarrhea including hormonal disorders, malnutrition, Hyperthyroidism, etc.

Keep in mind that diarrhea is not a disease in itself but a symptom of something. In other words, when you have diarrhea, your body is telling you that something is wrong. Occasional diarrhea, with a known cause, for example in the case of dehydration and stress,  is nothing to worry about. But if you have persistent diarrhea which last several days with no clear cause, you should consult your doctor who will determine the underlying cause of your problem.

To learn more about what to do when you have diarrhea, please check out our full dossier on the subject:

What To Eat When You Have Diarrhea

10 Tips To Prevent And Treat Diarrhea

Jenny Zhang

Jenny holds a Master's degree in psychiatry from the University of Illinois and Bachelors's degree from the University of Texas in nutritional sciences. She works as a dietician for Austin Oaks Hospital in Austin, Texas. Jenney writes content on nutrition and mental health for the Scientific Origin.