Causes

A number of diseases and conditions can cause diarrhea, including:

• Viruses. Viruses that can cause diarrhea include Norwalk virus (also known as norovirus), enteric adenoviruses, astrovirus, cytomegalovirus and viral hepatitis. Rotavirus is a common cause of acute childhood diarrhea. The virus that causes coronavirus disease 2019 (COVID-19) has also been associated with gastrointestinal symptoms, including nausea, vomiting and diarrhea.
• Bacteria and parasites. Exposure to pathogenic bacteria, such as E. coli or parasites through contaminated food or water, leads to diarrhea. When traveling in developing countries, diarrhea caused by bacteria and parasites is often called traveler's diarrhea. Clostridioides difficile (also known as C. diff) is another type of bacterium that causes diarrhea, and it can occur after a course of antibiotics or during a hospitalization.
• Medications. Many medications, such as antibiotics, can cause diarrhea. Antibiotics alleviate infections by killing bad bacteria, but they also kill good bacteria. This disturbs the natural balance of bacteria in your intestines, leading to diarrhea or a superimposed infection such as C. diff. Other drugs that cause diarrhea are anti-cancer drugs and antacids with magnesium.
• Lactose intolerance. Lactose is a sugar found in milk and other dairy products. People who have difficulty digesting lactose have diarrhea after eating dairy products. Lactose intolerance can increase with age because levels of the enzyme that helps digest lactose drop as you get older.
• Fructose. Fructose is a sugar found naturally in fruits and honey. It's sometimes added as a sweetener to certain beverages. Fructose can lead to diarrhea in people who have trouble digesting it.
• Artificial sweeteners. Sorbitol, erythritol and mannitol — artificial sweeteners are nonabsorbable sugars found in chewing gum and other sugar-free products — can cause diarrhea in some otherwise healthy people.
• Surgery. Partial intestine or gallbladder removal surgeries can sometimes cause diarrhea.
• Other digestive disorders. Chronic diarrhea has a number of other causes, such as IBS, Crohn's disease, ulcerative colitis, celiac disease, microscopic colitis and small intestinal bacterial overgrowth (SIBO).