Diarrhea is usually caused when the fluids within the intestines are not reabsorbed by the gut walls. This leads to loose, watery stools. Watery stools may also result from excessive water secretion from the intestines into the lumen or bowel.

Acute and chronic diarrhea

Diarrhea may be acute or chronic. Most cases of diarrhea begin suddenly and usually resolve on their own within a day or two.

Diarrhea lasting for more than two days may be problematic. Diarrhea is called chronic when it lasts for at least four weeks. This is usually due to some underlying functional or systemic disorder.

Causes of acute diarrhea

Diarrhea is a symptom of an underlying infection of the gastrointestinal tract rather than a disease in itself. Gastrointestinal infection may be caused by infections due to:-

Bacteria

Common bacteria that may cause diarrhea include Clostridium difficile (C. difficile), Escherichia coli (E. coli), Salmonella, Campylobacter and Shigella. These may all cause food poisoning and occur due to eating or consuming contaminated food or water. When gastroeneteritis occurs to travellers to developing countries in Africa, Asia, Latin America, and the Caribbean, it is termed Traveller’s diarrhea.

Viruses

Several viruses may give rise to serious acute episodes of diarrhea. These include norovirus, rotavirus, herpes simplex virus, cytomegalovirus, hepatitis virus etc.

Parasites or intestinal worms

These agents are also notorious is causing diarrhea in children and in some adults. Some of the parasites that may cause diarrhea include Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.

Other causes of short term acute diarrhea include:-

• Emotional changes and anxiety may also give rise to short episodes of diarrhea
• Food intolerance and allergies
• Excessive alcohol consumption or excessive coffee
• Appendicitis
• After radiation therapy
• Due to side effects of medications. Medications that are commonly implicated in causing diarrhea include antibiotics, magnesium containing antacids, non steroidal anti-inflammatory drugs (pain relievers), selective serotonin uptake inhibitors or SSRIs (used as antidepressants), cholesterol lowering agents like statins, purgatives that are used to empty the bowels, medicines used in cancer chemotherapy etc.
• Damage to the intestines due to reduced blood supply as seen in hernias

Causes of chronic diarrhea

Chronic diarrhea usually lasts over 4 weeks and may be caused by an underlying gastrointestinal or systemic disease. Some of the causes include:-

• Irritable bowel syndrome
• Crohn’s disease
• Coeliac disease
• Diabetes - especially diabetic gastroparesis (a complication of long term diabetes)
• Cystic fibrosis
• Lactose intolerance or milk intolerance
• Diverticular disease
• After a gastrectomy operation
• Chronic pancreatitis
• Colitis and ulcerative colitis – Inflammatory bowel diseases including ulcerative colitis and Crohn’s disease may cause chronic bloody diarrhea or frequent presence of blood in the stools.
• Cancer of the colon or rectum or presence of polyps
• Ischemic or loss of blood supply to a part of the gut
• Malabsorption syndromes may lead to chronic fatty or oily diarrhea. The stools are bulky, greasy or very bad smelling