Watery diarrhea can be caused by viral gastroenteritis, bacterial or parasitic infections, or lactose intolerance. It can also result from certain health conditions, such as celiac disease or irritable bowel syndrome.

This type of diarrhea is characterized by stools that are liquid like water and occur at least three times a day. It can sometimes appear as explosive diarrhea and may be accompanied by other symptoms, such as abdominal pain, nausea, fever, or changes in stool color, including yellow, brown, or black.

It is important to see a gastroenterologist whenever watery diarrhea occurs in order to identify the cause, receive proper treatment, and prevent complications such as dehydration.

female provider facing a female patient who is seated on the exam table with her hand on her abdomen

Main causes

Common causes of watery diarrhea include:

1. Viral gastroenteritis

Viral gastroenteritis can cause watery diarrhea and abdominal pain, along with nausea and vomiting, which can last for up to 7 days if not treated properly.

Viral gastroenteritis is caused by viruses such as rotavirus, norovirus, astrovirus, or adenovirus, which are commonly transmitted through contaminated food or water.

What to do: Stay well-hydrated by drinking plenty of water or oral rehydration solutions, get enough rest, and eat small, light meals such as toast, bananas, or rice. If diarrhea does not improve after 2 days, or if it affects children or older adults, consult a primary care provider or a gastroenterologist for the appropriate treatment.

2. Bacterial infections

Watery diarrhea can also result from bacterial infections and may be accompanied by abdominal cramps, nausea, vomiting, headache, fever, or blood in the stool.

The main bacteria that can cause watery diarrhea include Salmonella sp., Eschericia coli (E. coli), and Shigella sp., which are transmitted through the consumption of contaminated food or water.

What to do: Drink plenty of fluids and maintain a light diet. It is important to see a doctor to determine the type of bacteria and begin treatment with antibiotics, if necessary.

3. Parasitic infections

Parasites such as Giardia lamblia, Ascaris lumbricoides, and Entamoeba histolytica can also cause watery diarrhea and abdominal pain, along with nausea, vomiting, blood in the stool, fever, or fatigue.

In infections caused by Giardia lamblia (giardiasis), watery diarrhea may appear yellow and can range from severe and acute to mild and persistent.

What to do: See a gastroenterologist or primary care doctor for treatment, which typically involves antiparasitic medications such as metronidazole, tinidazole, albendazole, or mebendazole, depending on the type of parasite identified.

4. Lactose intolerance

Lactose intolerance can cause watery diarrhea and abdominal pain that develop a few hours after consuming dairy products. It may also be accompanied by excessive gas or nausea.

This condition occurs due to a deficiency or absence of the enzyme lactase, and the severity of symptoms can vary depending on the degree of intolerance.

What to do: Avoid consuming dairy products such as cow’s milk, goat’s milk, cheese, yogurt, and whey protein. A gastroenterologist can confirm the diagnosis and recommend lactase enzyme supplements to help digest lactose. During episodes of watery diarrhea, stay hydrated by taking regular small sips of water or oral rehydration solutions.

5. Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by inflammation of the intestinal lining that can cause alternating periods of watery diarrhea and constipation.

Other symptoms include abdominal pain, bloating, and excessive gas. The exact cause of IBS is not fully understood, but symptoms often worsen during times of stress or anxiety.

What to do: Treatment should be guided by a gastroenterologist and may include dietary changes and medications such as probiotics and low-dose antidepressants to relieve pain and other symptoms. Managing stress can also help prevent symptom flare-ups or worsening.

6. Celiac disease

Watery diarrhea that is yellow, light brown, or gray in color can be caused by celiac disease. It may also appear greasy, foamy, and have a strong odor.

Celiac disease is a severe gluten intolerance that causes inflammation and poor nutrient absorption when gluten-containing foods such as wheat, rye, or barley are consumed. This reaction increases the speed of bowel movements and the fat content in stools.

People with celiac disease usually notice an improvement in symptoms once gluten is eliminated from their diet.

What to do: Consult a gastroenterologist to confirm the diagnosis and begin a gluten-free diet. In some cases, a doctor may also prescribe immunosuppressive medications.

7. Crohn’s disease

Crohn’s disease is a chronic inflammation of the intestinal lining that can be triggered by genetic factors or immune system dysfunction.

It can cause watery diarrhea that may appear yellow due to poor nutrient absorption, along with abdominal pain or stools containing blood or mucus.

What to do: Treatment should be managed by a gastroenterologist and typically involves corticosteroids, immunosuppressants, or biologic therapy, along with dietary adjustments. In more severe cases, surgery may be needed to remove damaged sections of the intestine.

8. Ulcerative colitis

Ulcerative colitis is an inflammation of the intestinal lining that can cause bleeding or ulcers, leading to watery diarrhea with blood or mucus, or dark-colored stools that have a strong odor.

This condition can cause chronic diarrhea and may also be accompanied by abdominal pain, mucus in the stool, fever, excessive gas, or anemia.

What to do: Treatment should be managed by a gastroenterologist and depends on the severity of symptoms. It may involve immunosuppressive medications, biologic therapy, or, in some cases, surgery.

Warning signs

It is important to see a primary care provider or gastroenterologist when watery diarrhea:

Does not improve after 1 or 2 days, or if symptoms worsen;
Contains blood, mucus, or pus;
Appears yellow, green, dark brown, or black;
Occurs with fever;
Causes severe abdominal pain;
Leads to weight loss.

Go to the hospital immediately if signs of dehydration appear, such as headache, fatigue, dry mouth, reduced urination, confusion, or heart palpitations. These symptoms indicate a medical emergency that requires immediate treatment.

Watery Diarrhea: 8 Possible Causes (& What to Do)