Diarrhea is a problem everyone is familiar with - it is one of the most common reasons for people to seek medical advice1 - but it can range from being a mild, usually temporary condition, to one that can threaten life.
It is estimated that there are 2 billion cases of diarrheal disease every year globally, and that 1.9 million children below the age of 5 years, mostly in developing countries, die annually.2
The British English for diarrhea is diarrhoea.
Diarrhea should not be confused with the frequent passing of stools of normal consistency - this is not diarrhea. Diarrhea is instead characterized by abnormally loose or watery stools.3
Similarly, breastfed babies often pass loose, pasty stools, which is normal and not diarrhea.3
Contents of this article:
You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on diarrhea
Here are some key points about diarrhea. More detail and supporting information is in the body of this article.
- Diarrhea is unusually loose or watery stools.
- The problem may be acute, persistent or chronic.
- Most cases are caused by infection with bacteria, viruses or parasites.
- So-called "functional" chronic diarrhea includes irritable bowel syndrome (IBS).
- Inflammatory bowel diseases (IBD) are causes of chronic diarrhea, including Crohn's disease and ulcerative colitis.
- Diagnosis is usually made clinically - that is, after a doctor "takes and history" and completes an examination.
- Further tests - including on a stool sample - may be appropriate in some cases.
- The priority of treatment is to correct dehydration with fluids and electrolytes.
- Antidiarrheal medications can reduce diarrheal output. Zinc supplement is effective in children.
- Nutritional and probiotic interventions can be tried against diarrhea.
How is diarrhea classified?
There are three forms of diarrhea defined by the length of time that the condition lasts:1,2,4
- Acute diarrhea is short-lasting - between several hours and a number of days, and for less than 2 weeks or 14 days. World guidelines further say that acute diarrhea is the presence of 3 or more abnormally loose or watery stools in the preceding 24 hours. Acute diarrhea includes cholera. If the acute diarrhea is bloody, it is called dysentery
- Persistent diarrhea lasts for longer than 2 weeks but less than 4 weeks
- Chronic diarrhea lasts more than 4 weeks.
Most people think of diarrhea in terms of stool consistency - how watery it is. This may be the best concept also recognized by clinicians, who additionally define it in terms of stool frequency, consistency, volume or weight.5
For example, some definitions cite a daily stool weight greater than 200 grams a day - but there can be great variety between different people's normal bowel motions.5
Perhaps the simplest definition of diarrhea is the passage of loose stools more frequently than is usual for the individual.4
The pathophysiology of diarrhea further defines it. There are four mechanisms by which the condition occurs, and there can be overlap between these in individual cases:1
- Osmotic diarrhea occurs when the small intestine cannot absorb a soluble compound and fluid is drawn into the gut
- Secretory diarrhea results from active chloride secretion into the bowel. Water follows the chloride ions, leading to a net loss of fluid
- Inflammation of the intestinal lining
- Motility of the intestines is increased.
Causes of diarrhea
Most cases of diarrhea are the symptom of an infection in the gastrointestinal tract.4
The microbes causing gastrointestinal infection that leads to diarrhea include:4
- Parasitic organisms.
The most commonly identified causes of acute diarrhea in the US are the bacteria Salmonella, Campylobacter, Shigella and Shiga toxin-producing Escherichia coli.6
There are cases of chronic diarrhea that are labeled "functional" because they cannot be not explained by structural or biochemical abnormalities.7
In the developed world, irritable bowel syndrome (IBS) is the most common cause of functional diarrhea.7,8
IBS is a complex of symptoms usually diagnosed by a process of elimination of other possible problems. There is cramping abdominal pain and altered bowel habit, either with diarrhea or constipation.7,8
Inflammatory bowel disease (IBD) is another cause of chronic diarrhea, in which case the diagnosis will be either ulcerative colitis or Crohn's disease, and there is often blood and pus in the stool in both conditions.8
Other major causes of chronic diarrhea include:8
- Microscopic colitis - this is secretory diarrhea usually affecting older people. There is microscopic inflammation, with changes visible on microscopy of a colon biopsy. The persistent diarrhea is often during the night
- Malabsorptive and maldigestive diarrhea - the first is caused by impaired nutrient absorption, the second by impaired digestive function. Celiac disease is one example
- Chronic infections - these diarrheas are persistent whereas most infectious causes lead to acute diarrhea. A history of travel or antibiotic use are clues, and numerous bacteria and parasites are culprits. These cases are primarily inflammatory, although malabsorption is caused by giardiasis, a parasitic infection
- Drug-induced diarrhea - the obvious cause is laxatives, but a list of other drugs also leads to diarrhea - check medications with a pharmacist or doctor
- Endocrine causes - chronic secretory diarrhea can have a range of hormone system causes, including Addison disease, carcinoid tumors. Meanwhile, hyperthyroidism can increase gut motility
- Cancer causes - neoplastic diarrhea is associated with a number of gut cancers.
On the next page we look at the symptoms of diarrhea and how diarrhea is diagnosed. On the final page we discuss the available treatments and ways in which to prevent diarrhea.