Normally, the food you eat remains in liquid form during most of the digestive process. When the unabsorbed food residue passes through your colon, most of the fluids are absorbed and what remains is a semisolid stool.
In diarrhea, the food and fluids you ingest pass too quickly or in too large an amount â€” or both â€” through your colon. The fluids aren't sufficiently absorbed, and the result is a watery bowel movement. In addition, the lining of your colon may be inflamed or diseased, making it less able to absorb fluids.
The most common causes of diarrhea include:
Viruses. Common viruses that cause diarrhea are Norwalk virus, cytomegalovirus, viral hepatitis and the herpes simplex virus. Rotavirus is the most common cause of acute childhood diarrhea. Viral diarrhea spreads easily.
Bacteria and parasites. Contaminated food or water can transmit bacteria and parasites to your body. Parasites such as Giardia lamblia and cryptosporidium can cause diarrhea. Common bacterial causes of diarrhea include campylobacter, salmonella, shigella and Escherichia coli. Diarrhea caused by bacteria and parasites can be common when traveling in developing countries, and is often called traveler's diarrhea.
Medications. Many medications can cause diarrhea. The most common are antibiotics.
Antibiotics destroy both good and bad bacteria, which can disturb the natural balance of bacteria in your intestines. This disturbance sometimes leads to an infection with bacteria called Clostridium difficile, which can also cause diarrhea.
Lactose. A sugar found in milk and milk products, lactose is a common cause of diarrhea in some people.
Fructose. Fructose, a sugar found in many fruits, is a common cause of diarrhea, especially in children.
Artificial sweeteners. Sorbitol and mannitol, artificial sweeteners found in chewing gum and other sugar-free products, can cause diarrhea in some otherwise healthy people.
Surgery. Some people may experience diarrhea after undergoing abdominal surgery or gallbladder removal surgery.
Other digestive disorders. Chronic diarrhea has a number of other causes, such as Crohn's disease, ulcerative colitis, celiac disease and irritable bowel syndrome.