Causes and Risk Factors of Diarrhea

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Diarrhea is a common problem that can come on suddenly or be a chronic complaint. The possible causes of diarrhea include food poisoning, infections, food allergies or intolerances, and medication. Some conditions that cause chronic diarrhea run in families or, rarely, have a genetic basis. You can reduce your risk of acute diarrhea by learning good food safety and cleanliness habits, whether at home or while traveling.

causes of diarrhea
Illustration by Brianna Gilmartin, Verywell 

Common Causes

The most common cause of diarrhea, especially diarrhea that starts suddenly (acute diarrhea), 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:

  • Food poisoning
  • Traveler's diarrhea
  • Stomach flu

You may also have acute diarrhea due to side effects of medications, including antibiotics, antacids that contain magnesium, and cancer treatment medications.

Children are especially at risk for diarrhea as they tend to put objects in their mouths and may not have developed good handwashing habits. They are at high risk of dehydration from diarrhea, so they should be seen by a doctor.

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, improper food handling, 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

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 diarrhea and recently traveled to a less-developed country or drank untreated water from a stream, river, or pond (in the U.S. or elsewhere), 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 mucus or blood
  • Other symptoms: Possibly vomiting and/or fever

Stomach Flu

Stomach flu, also known as gastroenteritis, is caused by a virus, but not the same that causes seasonal flu (influenza). Examples of viruses that can cause stomach flu are rotavirus and norovirus. 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.

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

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

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

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

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

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

Medication

Some medications, in particular antibiotics and chemotherapy, can cause diarrhea, as well as laxatives containing magnesium. 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.

Genetics

There are congenital diarrheal disorders linked to specific genes. These disorders usually come on in the first few months of a child's life. They are often most common in certain populations, although congenital chloride diarrhea is one that appears worldwide.

Some other conditions that may display chronic diarrhea also tend to run in families, including celiac disease, some forms of lactose intolerance, and food allergies.

Lifestyle Risk Factors

A change to your diet, such as going on a mostly liquid diet, eating too much fruit or fiber, or eating spicy foods may lead to diarrhea.

Food poisoning, one of the leading causes of diarrhea, is often caused by improper food handling.

These four habits can reduce your risk of food poisoning, according to the Centers for Disease Control:

  • Clean: Keep your kitchen clean, wash utensils and cutting boards with hot, soapy water.
  • Separate: Raw meat, seafood, poultry, and eggs should be kept separate from other food. Use a separate cutting board for these.
  • Cook: Use a food thermometer to ensure meat is cooked to an internal temperature that will kill the bacteria that cause food poisoning.
  • Chill: Don't let food be in the danger zone between 40 F and 140 F for more than two hours. Thaw frozen foods in the refrigerator or microwave, not out on the counter. Be sure your refrigerator is kept below 40 F.

The bacteria, viruses, and parasites that cause traveler's diarrhea and stomach flu are spread by contact with contaminated surfaces, food, and water. In the medical world, this is called the fecal-oral route. To reduce your risks, wash your hands well after using the bathroom, changing your child's diapers, and before eating. If you don't have access to soap and water, use an alcohol-based hand gel.

Never drink untreated water from a natural source, such as a stream. Even in developed countries, they can be contaminated with diarrhea-causing parasites spread by wildlife, such as Giardia. When traveling to areas that have a higher risk of contaminated water and food, drink only bottled water and don't use ice unless it is from bottled or purified water. Avoid uncooked vegetables and fruits (unless they can be peeled), raw shellfish, undercooked meat, and dairy products.

Sometimes the cause of diarrhea is taking too many laxatives or longer-term abuse of laxatives.

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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