It can be unpleasant and debilitating, but it is important to note that diarrhea is a symptom – not a disease. In most cases, it is short-lived and self-limiting.

But if you have chronic diarrhea, it is imperative to establish the underlying cause.

Diarrhea is defined as stool output in excess of 300 grams a day and in increase in the fluidity of stool. Diarrhea occurs when you have a bowel transit time that is too fast. Faeces don’t sit in the colon long enough for water to be absorbed back into your body, so the stool comes out runny. If you have chronic diarrhea, you are not receiving the maximum benefits from foods because you are not absorbing all the nutrients. Loss of fluids and electrolyte minerals can cause weakness and disorientation.

In infants, small children and the elderly, dehydration can be dangerous, and happen suddenly.

Most diarrhoea is self-limiting – it’s the body’s way of getting rid of something it doesn’t like – foods, microbes, toxins.

But if you have severe abdominal or rectal pain, fever, blood in your stool, signs of dehydration (dry mouth, anxiety, excessive thirst, severe weakness, dizziness) – or your diarrhea lasts more than three days – see your doctor. Caution should be taken with babies, small children, the elderly and anyone who is ill or recovering from an illness.

Chronic diarrhea can be caused by – drugs, diverticular disease, foods or beverages that disagree with your digestive system, food intolerances (such as lactose intolerance or fructose intolerance), infections (bacterial, fungal, viral, or parasitic), IBS (irritable bowel syndrome), IBD (inflammatory bowel disease), malabsorption, laxative use and abuse, contaminated water supply, diseases such as cancer and AIDS. People with gallbladder problems often experience diarrhea after a fatty meal.

Many substances can cause diarrhea, including an excess of vitamin C and magnesium. Antacids that contain magnesium salts can cause diarrhea. Sorbitol, mannitol and xylitol are “sugars” found in “sugar-free” gums and lollies – these can often cause diarrhea, even in small amounts, in sensitive individuals.

While constipation is a common cause of hemorrhoids, long-term diarrhea can also contribute to the condition, caused by straining and vascular weakness.

Causes Of Diarrhea

Diarrhea may be due to a disturbance in osmosis, secretion, or motility of the bowel; sometimes it is caused by a combination of two or more problems.

Osmotic diarrhea

The small and large intestines are lined with a semipermeable membrane. Fluid normally diffuses through the membrane and an equal osmotic pressure is maintained on either side. Food particles that cannot be absorbed by the intestine exert osmotic pressure and cause fluid from the bloodstream to cross the lining to try to balance the fluid concentration on either side. This excess fluid in the intestine produces diarrhoea.

People who frequently consume magnesium containing antacids, such as Mylanta, or laxatives, such as milk of magnesia, may have an osmotic diarrhoea because the magnesium cannot be absorbed by the intestine and will exert a strong osmotic force.

People who have lactose deficiency (milk intolerance) also have problems with diarrhoea. In this case, the milk sugar lactose cannot be absorbed by the small intestine. Bacteria in the colon break the lactose into simple sugars, which then exert an osmotic force in the colon, resulting in loose stools.

Fasting will generally improve osmotic diarrhoea since the osmotically active agent will be eliminated.

Secretory diarrhea

As food passes through the GI tract, the cells lining the inside of the tube absorb fluid and nutrients and pass them into the bloodstream. These same cells also secrete fluid from the bloodstream into the interior of the GI tract.

Normally, intestinal cells absorb more fluid than they secrete, and there is a “net absorption”. However, sometimes things can go awry and the cells secrete excessive fluid, causing a “net secretion” and diarrhea. In this case, even fasting will not stop the diarrhea.

Certain bacteria such as the cholera bacteria, vibrio cholerae, salmonella, and escherichia coli (the cause of traveller’s diarrhea) give off toxins that can stick to the intestinal lining. Although these toxins do not damage the intestinal lining, they do cause the cells to secrete massive amounts of fluid, which results in voluminous watery diarrhea typical of food poisoning. This is a common cause of acute severe diarrhoea.

Some rare endocrine tumours give off hormones (for example, vipoma) or the chemical serotonin (carcinoid tumours), which cause intestinal secretion. In this case, diarrhoea doesn’t improve and requires specialised treatments.

Any disease that damages the lining of the intestine, such as Crohn’s disease, a common form of inflammatory bowel disease, tends to impair absorption and leads to net secretion and diarrhea.

Motility disorders

The normal contractions, or motility, of the small intestine act like a cleansing wave to prevent stagnation of fluid and overgrowth of bacteria. Certain diseases such as long-standing diabetes and scleroderma can affect the nerves and muscles of the intestine, so that bowel contents move sluggishly along the gastrointestinal tract, giving bacteria the opportunity to multiply. As bacteria compete for food they impair absorption of nutrients and can cause weight loss and diarrhea.

Some people with irritable bowel syndrome have a colonic motility problem, which may lead to diarrhoea, although many people with irritable bowel syndrome have normal colonic motility. In developed countries, irritable bowel syndrome remains the most common cause of chronic diarrhea in women.

Complex causes of diarrhea

In certain instances, diarrhoea may be caused by all of these problems working in unhappy concert. In patients with Crohn’s disease, for example, the last portion of the small intestine, the ileum, is often inflamed (ileitis). This means that bile from the liver cannot be absorbed normally and travels instead into the large intestine, where it stimulates secretion of fluid and leads to secretory diarrhoea. Because the small intestine is inflamed, lactase production is impaired, which results in milk intolerance and loose stools (osmotic diarrhea). Prolonged inflammation can lead to scarring and the bowel can become obstructed, interfering with normal motility. For such complex causes, treatment must also be diverse – there is the need to decrease inflammation, bind bile salts, and/or supress bacterial growth.

Acute diarrhea

Diarrhea that has been present for less than two weeks is usually referred to as acute diarrhea. Most infectious causes of diarrhea (viral or bacterial), are self-limited infections and, even without treatment, resolve within days.

Most cases of diarrhoea are not too serious. Sudden onset of diarrhoea associated with fever, vomiting, and cramping pains in the stomach is often caused by flu or other viruses (viral gastroenteritis).

Food poisoning, another common cause of diarrhoea, is caused by bacteria, or toxins produced by bacteria, that have overgrown in food and find their way into the GI tract. Foods with high protein content such as meat, chicken, fish, and eggs more readily support overgrowth of bacteria than do carbohydrates. Dry foods are also less likely to cause food poisoning. One important key to prevention is refrigeration – food should never be allowed to sit without refrigeration for more than three hours.

Acute diarrhoea can also be caused by parasites. Amebic dysentry caused by the parasite Entamoeba histolytic is a common cause of diarrhoea, especially in developing nations, where the water supply may be contaminated. Most often amoebic dysentery is a self-limited disease. Occasionally, if it is not treated appropriately, patients can develop severe complications, including a liver abscess.

Another common water supply contaminant is giardia lamblia. Individuals who drink water from mountain streams or use all water are prone to develop giardiasis. Although in most cases Giardiasis is a self-limited acute disease, some individuals, especially those with impaired immune systems, may go on to chronic infection and present with symptoms similar to malabsorption with weight loss.

Chronic diarrhea

When diarrhoea persists beyond 2 to 4 weeks, it is referred to as chronic diarrhea. Since most of the common infectious causes of diarrhoea are self-limited and last only a few days, diarrhoea that continues beyond two weeks often is caused by other diseases. Most of the time your doctor will start by ordering stool tests, including routine culture, examination for ova and parasites, and assay for Clostridium difficile, the cause of antibiotic-related diarrhoea. If you have lost weight and have diarrhoea, the doctor will probably check your stool for the presence of fat, which would indicate you are either not absorbing food (disease of the small intestines) or not digesting your food (your pancreas is not making digestive enzymes).

If these stool tests are negative, in all likelihood your doctor will recommend either a sigmoidoscopy or a colonoscopy to rule out inflammatory bowel disease. An upper GI series, including an X-ray of your small intestine, may also be ordered. Examples of disorders that lead to chronic diarrhoea include irritable bowel syndrome, inflammatory bowel disease (ulcerated colitis and Crohn’s disease), and certain bowel infections (giardiasis, amoebiasis, Clostridium difficile-related colitis).

Occasionally people will develop diarrhoea after they have had their gallbladder removed.

Remember you should always see your doctor if you develop severe diarrhoea or the diarrhoea persists beyond two weeks.

Diarrhea caused by drugs

Just about any drug can cause diarrhoea. If you are taking medication, ask your doctor if it could be causing your diarrhea.

Antibiotics may cause diarrhoea because they change the normal flora of the colon, permitting overgrowth of certain toxic bacteria. Mild diarrhoea caused by antibiotics may be treated by probiotics. Usually the diarrhea improves by itself after stopping the antibiotic, but if it is severe or persists, consult your doctor.

The cause of antibiotic-related diarrhoea and antibiotic-related colitis is the bacterium Clostridium difficle. This bacteria is usually not detectable in the stool of normal individuals, but when normal bacteria are suppressed by antibiotics this bacterium may grow and cause problems. C. difficile gives off a toxin that damages the lining of the colon and can cause fever, lower abdominal cramps, and severe diarrhoea. If not treated the patient could not go on to require surgery for a bowel perforation. If you have diarrhoea and have taken antibiotics in the recent past or are currently on antibiotics, your doctor will probably order a stool test for the bacterium Clostridium difficile.

C. difficile related diarrhoea has now become the most common cause of diarrhea in hospitalised patients. Although usually associated with a course of antibiotics, the organism can also be transmitted from patient to patient. Therefore, the washing of hands and good hygiene practices are even more important. Hospital epidemics of Clostridium difficile diarrhea are well documented.