What causes Diarrhea ?
Acute diarrhea is usually caused by a bacterial, viral, or parasitic infection. Chronic diarrhea is usually related to a functional disorder such as irritable bowel syndrome or an intestinal disease such as Crohns disease.
                
The most common causes of diarrhea include the following:
                
- Bacterial infections. Several types of bacteria consumed through contaminated food or water can cause diarrhea. Common culprits include Campylobacter, Salmonella, Shigella, and Escherichia coli (E. coli).  - Viral infections. Many viruses cause diarrhea, including rotavirus, norovirus, cytomegalovirus, herpes simplex virus, and viral hepatitis. Infection with the rotavirus is the most common cause of acute diarrhea in children. Rotavirus diarrhea usually resolves in 3 to 7 days but can cause problems digesting lactose for up to a month or longer.  - Parasites. Parasites can enter the body through food or water and settle in the digestive system. Parasites that cause diarrhea include Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.  - Functional bowel disorders. Diarrhea can be a symptom of irritable bowel syndrome.  - Intestinal diseases. Inflammatory bowel disease, ulcerative colitis, Crohns disease, and celiac disease often lead to diarrhea.  - Food intolerances and sensitivities. Some people have difficulty digesting certain ingredients, such as lactose, the sugar found in milk and milk products. Some people may have diarrhea if they eat certain types of sugar substitutes in excessive quantities.  - Reaction to medicines. Antibiotics, cancer drugs, and antacids containing magnesium can all cause diarrhea.
                
Some people develop diarrhea after stomach surgery, which may cause food to move through the digestive system more quickly.
                
People who visit certain foreign countries are at risk for travelers diarrhea, which is caused by eating food or drinking water contaminated with bacteria, viruses, or parasites. Travelers diarrhea can be a problem for people traveling to developing countries in Africa, Asia, Latin America, and the Caribbean. Visitors to Canada, most European countries, Japan, Australia, and New Zealand do not face much risk for travelers diarrhea.
                
In many cases, the cause of diarrhea cannot be found. As long as diarrhea goes away on its own within 1 to 2 days, finding the cause is not usually necessary.