What Are The Causes Of Diarrhea in Adults

Diarrhea is the frequent passing of large volumes of loose stools; it is not a disease, but a symptom caused by some other digestive disorder.

Bowel movements as frequent as three to five times a day may be normal for some people, as is large amount feces in those who consume a lot of vegetables. Rather than the volume of stools or the frequency of passing them, it is the watery consistency of the stool that determines whether it is diarrhea. Diarrhea is often accompanied by stomach cramps, gas and the inability to control or delay the bowel movements. If a toxin or an infection is causing the diarrhea, nausea and vomiting may also be present.

Complications: Dehydration is a major complication of diarrhea as large quantities of fluid is lost with each bowel movement. If vomiting is also present, it can quickly deteriorate to dangerous levels, especially in very young patients, older people and those who are already weak. Along with fluids, essential minerals necessary for normal body functions such as potassium, sodium, magnesium etc. are also lost, causing chemical imbalance in the body. Severe dehydration can result in low blood pressure leading to syncope or fainting. It may cause abnormal heart rhythms and several other disorders which can become dangerous.


Diarrhea can be considered as either acute or chronic, based on the duration of the abnormal condition; their causes also may be different.

Acute diarrhea which lasts for only a few days may be caused by viral or bacterial infections or other parasitic infestations. The toxins produced by them or other poisonous substances ingested by the patient as well as the use of certain drugs may also cause acute diarrhea.

Chronic diarrhea, on the other hand, continues for over a week or more. It is often caused due to the following:

The treatment for chronic diarrhea is focused on treating the cause which may be chronic as well.

Types of diarrhea

Diarrhea can be classified as rapid transit diarrhea, osmotic diarrhea and secretory diarrhea depending on the reason of its origin. Stool normally contains sixty to ninety percent water when it is eliminated. Once the digestion of food and absorption of nutrients are over, the remaining waste materials become the stool. As the stool passes through the large intestine, excess water is reabsorbed into the body, giving it a solid to semi solid texture. However, stool may remain watery, if enough water is not removed from it. The reason for poor re absorption of water from the stool can vary. It may be because the stool passed too quickly through the intestines or contained substances which impede the absorption of water by the large intestine. When intestines secrete too much water due to some reason, it is excreted as watery stools.

Rapid passage of stool through the last section of the digestive tract often causes frequent diarrhea. Unless the stool remains in the large intestine for a sufficient amount of time for the re absorption of water, its consistency may become too watery. Hyperthyroidism and a condition called Zollinger-Ellison syndrome, resulting from tumor induced overproduction of stomach acids, cause rapid transit of stool. If parts of the digestive tract such as stomach and the intestines have been removed surgically, or bypassed, the stool may move too fast. Ulcerative colitis and such other inflammatory bowel diseases, the use of laxatives, antacids with magnesium compounds, the hormone serotonin and prostaglandins are also reasons for quick passage of the stool, resulting in diarrhea. Generally, highly acidic foods and those with high sugar content can accelerate the bowel movements. Certain specific foods, anxiety and stress also induce diarrhea in some people.

Osmotic diarrhea is watery stools resulting from the presence of some substances which remain unabsorbed by the walls of the colon. The continued presence of these substances leads to diarrhea, due to the retention of excess amounts of water in the colon. Certain food additives such as mannitol, hexitols sorbitol and other chemicals used as a substitute for sugar in products intended for diabetics and dieters cause osmotic diarrhea. Certain types of beans and fruits are also known to result in this condition.

Lactose intolerance is a condition developing in people who lack an enzyme called lactase which breaks down the milk sugar lactose into the simpler sugar glucose and another sugar called galactose, for absorption by the small intestine. In the absence of lactase, the milk sugar lactose remains in the intestine. Use of milk and milk products by lactose intolerant people results in osmotic diarrhea. When people with lactose intolerance stop taking lactose containing foods, their osmotic diarrhea gets resolved eventually.

The presence of blood in the stomach or the intestines also causes osmotic diarrhea. The blood may have come from a leaking ulcer in the stomach or intestine. When the normal bacteria of the digestive tract are destroyed by the use of antibiotics, new types of bacteria take their place and it may be another reason for osmotic diarrhea. Excessive growth of the normal bacteria in the intestine also may cause it.

Secretory diarrhea results from the excess secretion of water and salts like sodium chloride by the intestines. Viral infections, certain bacterial infections by Campylobacter, cholera or parasitic infestations and toxins secreted by certain organisms induce excess secretion by the intestines. Castor oil, strong laxatives and excess bile also irritate the intestines into secreting water and salts. Presence of tumors like vipoma or gastrinoma and polyps also may induce secretory diarrhea.

Inflammatory diarrhea is caused by the inflammation of the tissue lining the walls of the large intestine, resulting from infections like tuberculosis, auto immune conditions such as Crohn’s disease, cancers and tumors such as adenocarcinoma and lymphoma. When the lining of the large intestine is inflamed, it becomes less effective in absorbing water. The inflamed lining of the rectum has an increased sensitivity to stool and it makes the person feel an urgent need for frequent emptying of the rectum, resulting in diarrhea.


Diarrhea is a very common occurrence and not all episodes require immediate medical treatment. However, some cases may require urgent medical attention as there may be a chance of developing severe complications. It is advisable that the person assesses his condition before seeking medical help using the information given below.

 Warning signs: When diarrhea is accompanied by certain other symptoms, it may be necessary to seek medical attention. The following are some of the symptoms to watch out for:

  • Passing of either pus or blood along with stool
  • High body temperature
  • Development of severe dehydration with symptoms such as dryness of mouth, decrease in urine output, extreme lethargy and severe thirst
  • Severe abdominal pain
  • Frequent Diarrhea that continues for over a week
  • Occurrence of diarrhea even at night
  • Recent noticeable weight loss without apparent reason

 When any of the first four symptoms accompanies diarrhea, people should get urgent medical attention. They may have to be admitted in the hospital for immediate treatment and further investigations to detect the cause. Those who have the other warning signs also should see a doctor without much delay. Even without any of these accompanying symptoms, any diarrhea lasting for over three days requires medical attention. If it does not clear up with recommended medications, the doctor may decide whether further testing is necessary.

At the doctor’s clinic, a physical examination of the abdomen as well as the general condition of the patient is done with a view to assess the hydration levels and detect signs of developing complications. The patient may be asked about the previous medical history with emphasis on existing digestive disorders and the drugs used, including recent antibiotic therapy. Details about the severity, frequency and nature of diarrhea as well as the presence of other symptoms may help the doctor decide on the diagnostic tests and treatment required. Doctor may ask the patient about:

  • the specific circumstances in which the diarrhea started such as travels or change in food and water
  • the use of drugs and any recent change in medication as well as recent use of antibiotics
  • the presence of abdominal pain, nausea and vomiting
  • recent changes observed in the color and texture of stool and the presence of mucus, pus and traces of blood
  • loss of appetite or recent weight loss
  • frequency and urgency of bowel movements
  • occurrence of diarrhea in the locality or among the patient’s family and friends

Testing: Based on the physical examination and the previous medical history and other details provided by the patient, doctor may prescribe further testing to determine the cause or initiate general drug therapy. Rehydration measures which are immediately started may be sufficient for acute diarrhea of sudden onset, which is usually of viral origin. Without further testing or treatment, it may clear up in less than four days.

People who have blood in the stool and severe pain in the abdomen may require imaging tests to detect any abnormalities in the stomach and intestines. Stool is tested for the presence of microorganisms such as Giardia, Yersinia, shigella, Cryptosporidium, Campylobacter, amebas etc. Stool culture or specific enzyme tests may be necessary to detect certain microbes. Stool is tested for Clostridium difficile toxin if the patient has been on antibiotic therapy because those particular bacteria multiply when the normal microbes in the digestive tract are destroyed by antibiotics.

When diarrhea persists for more than a week, in addition to the above tests, colonoscopy may be done to detect any abnormality in the colon and rectum, which may be causing the diarrhea. Biopsy of the lining of the rectum may reveal inflammatory bowel disease. Presence of tumors, their size and location may be determined by a CT scan enterography. Pancreatic function and thyroid and adrenal gland functions are also tested, if necessary. Fat globules in the stool point to malabsorption of lipids. Breath analysis for the presence of hydrogen is done, if malabsorption of carbohydrates is suspected.

Treatment Of Diarrhea

Whenever the cause for diarrhea is identified, the cause is treated along with the symptoms. If the diarrhea is caused by any drug the person is taking, it is stopped or substituted with more suitable ones. Infestations are eradicated with appropriate drugs. If any tumor is found to be the cause, it can be surgically removed. Diarrhea due to viral infections clears up in a day or two without any treatment.

Rehydration: One of the major complications of diarrhea is severe dehydration due to the excessive fluid loss through watery stools, and by vomiting, if it is also present. Immediate measures should be taken to replenish the body with not only water but also with adequate amounts of salts and sugars which were also lost. Oral rehydration is possible once the vomiting has stopped. But in severe cases, electrolyte supplements are given intravenously for effective rehydration. Usually, severely dehydrated people are admitted in the hospital for rehydration therapy and for preemptive treatment of possible complications as well as for further diagnostic tests, if necessary.

Drugs: Anti diarrheal drugs like Loperamide and other prescription medication such as diphenoxylate, codeine, and opioid drugs relax the muscles of the intestine and help in slowing down diarrhea. They can be safely used by people who have watery stools but none of the other warning symptoms accompanying their diarrhea. However, these drugs are contraindicated in people with gastroenteritis of bacterial origin, as Shigellosis, Salmonellosis and infection by Clostridium difficile become worse with the use of anti diarrheal drugs.

Certain non-prescription drugs like kaolin-pectin function as adsorbents, adhering to toxins and other harmful chemicals as well as to microorganisms which cause infection. Some of them have the property of altering the texture of stool and firming it up. Bismuth salicylate, often used for treating diarrhea, may turn stools or tongue black, but it is a temporary side effect. Chronic diarrhea is often relieved by the use of methylcellulose and psyllium husk, which are more often used for relieving constipation by adding bulk to the stool.

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Yasser Elnahas

MD, PHD, Professor Of CardioVascular Surgery
Dr. Yasser Elnahas, Is an associate Professor of Cardiovascular Surgery. Dr. Elnahas was trained as a fellow At Texas Heart Institute And Mayo Clinic Foundation.Dr. Elnahas is dedicated to educating the general public about different disease conditions and simplifying the medical knowledge in an easy to understand terminology.

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