Diarrhea , additionally spelled diarrhoea , is the condition of having at least three loose or liquid bowel movements each day. It most often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration most often begin with loss of the normal stretchiness of the skin and irritable behaviour. This can progress to decreased urination, loss of skin color, a fast heart rate, and a decrease in responsiveness as it becomes more severe. Loose but non-watery stools in babies who're breastfed, however, might be normal. 
The most common cause is an infection of the intestines due to either a virus, bacteria, or parasite ; a condition known as gastroenteritis. These infections are most often acquired from food or water that has been contaminated by stool, or directly from another person who's infected. It might be divided into three types: short duration watery diarrhea, short duration bloody diarrhea, and if it lasts for more than two weeks, persistent diarrhea. The short duration watery diarrhoea might be due to an infection by cholera, although this is rare in the developed world. If blood is present it is additionally known as dysentery.  A number of non-infectious causes might additionally result in diarrhea, including hyperthyroidism, lactose intolerance, inflammatory bowel disease, a number of medications, and irritable bowel syndrome. In most cases, stool cultures aren't required to confirm the exact cause. 
Prevention of infectious diarrhoea is by improved sanitation, clean drinking water, and hand washing with soap. Breastfeeding for at least six months is additionally recommended as is vaccination against rotavirus. Oral rehydration solution (ORS), which is clean water with modest amounts of salts and sugar, is the treatment of choice. Zinc tablets are additionally recommended.  These treatments have been estimated to have saved 50 million children in the past 25 years.  When people have diarrhoea it is recommended that they continue to eat healthy food and babies continue to be breastfed.  If commercial ORS aren't available, homemade solutions might be used.  In those with severe dehydration, intravenous fluids might be required.  Most cases; however, can be managed well with fluids by mouth.  Antibiotics, while rarely used, might be recommended in a few cases like those who have bloody diarrhoea and a high fever, those with severe diarrhea following travelling, and those who grow specific bacteria or parasites in their stool.  Loperamide might help decrease the number of bowel movement but isn't recommended in those with severe disease. 
About 1.7 to 5 billion cases of diarrhoea occur per year.   It is most common in developing countries, where young children get diarrhoea on average three times a year.  Total deaths from diarrhoea are estimated at 1.26 million in 2013 – down from 2.58 million in 1990.  In 2012, it is the second most common cause of deaths in children younger than five (0.76 million or 11%).   Frequent episodes of diarrhoea are additionally a common cause of malnutrition and the most common cause in those younger than five years of age.  Other long term problems that can result include stunted growth and poor intellectual development. 
Secretory diarrhoea means that there's an increase in the active secretion, or there's an inhibition of absorption. There is little to no structural damage. The most common cause of this type of diarrhoea is a cholera toxin that stimulates the secretion of anions, especially chloride ions. Therefore, to maintain a charge balance in the lumen, sodium is carried with it, along with water. In this type of diarrhoea intestinal fluid secretion is isotonic with plasma even throughout fasting.  It continues even when there's no oral food intake.
Osmotic diarrhoea occurs when too much water is drawn into the bowels. If a person drinks solutions with excessive sugar or excessive salt, these can draw water from the body into the bowel and cause osmotic diarrhea.  Osmotic diarrhoea can additionally be the result of maldigestion (e.g., pancreatic disease or Coeliac disease), in which the nutrients are left in the lumen to pull in water. Or it can be caused by osmotic laxatives (which work to alleviate constipation by drawing water into the bowels). In healthy individuals, too much magnesium or vitamin C or undigested lactose can produce osmotic diarrhoea and distention of the bowel. A person who has lactose intolerance can have difficulty absorbing lactose after an extraordinarily high intake of dairy products. In persons who have fructose malabsorption, excess fructose intake can additionally cause diarrhea. High-fructose foods that additionally have a high glucose content are more absorbable and less likely to cause diarrhea. Sugar alcohols like sorbitol (often found in sugar-free foods) are difficult for the body to absorb and, in large amounts, might lead to osmotic diarrhea.  In most of these cases, osmotic diarrhoea stops when offending agent (e.g. milk, sorbitol) is stopped.
Exudative diarrhoea occurs with the presence of blood and pus in the stool. This occurs with inflammatory bowel diseases, like Crohn's disease or ulcerative colitis, and additional severe infections like E. coli or additional forms of food poisoning. 
Inflammatory diarrhoea occurs when there's damage to the mucosal lining or brush border, which leads to a passive loss of protein-rich fluids and a decreased ability to absorb these lost fluids. Features of all three of the additional types of diarrhoea can be found in this type of diarrhea. It can be caused by bacterial infections, viral infections, parasitic infections, or autoimmune problems like inflammatory bowel diseases. It can additionally be caused by tuberculosis, colon cancer, and enteritis.
If there's blood visible in the stools, it is additionally known as dysentery. The blood is trace of an invasion of bowel tissue. Dysentery is a symptom of, among others, Shigella , Entamoeba histolytica , and Salmonella .
Diarrheal disease might have a negative impact on both physical fitness and mental development. "Early childhood malnutrition resulting from any cause reduces physical fitness and work productivity in adults,"  and diarrhoea is a primary cause of childhood malnutrition.  Further, evidence suggests that diarrheal disease has significant impacts on mental development and health; it has been shown that, even when controlling for helminth infection and early breastfeeding, children who had experienced severe diarrhoea had significantly lower scores on a series of tests of intelligence.  
Acute diarrhoea is most commonly due to viral gastroenteritis with rotavirus, which accounts for forty percent of cases in children under five.  (p. 17) In travelers however bacterial infections predominate.  Various toxins like mushroom poisoning and drugs can additionally cause acute diarrhea.
Chronic diarrhoea can be the part of the presentations of a number of chronic medical conditions affecting the intestine. Common causes include ulcerative colitis, Crohn's disease, microscopic colitis, celiac disease, irritable bowel syndrome and bile acid malabsorption.
There are a large number of causes of infectious diarrhea, which include viruses, bacteria and parasites.  Infectious diarrhoea is frequently referred to as gastroenteritis.  Norovirus is the most common cause of viral diarrhoea in adults,  but rotavirus is the most common cause in children under five years old.  Adenovirus types 40 and 41,  and astroviruses cause a significant number of infections. 
Parasites, particularly protozoa (e.g., Cryptosporidium spp., Giardia spp., Entamoeba histolytica , Blastocystis spp., Cyclospora cayetanensis ), are frequently the cause of diarrhoea that involves chronic infection. The broad-spectrum antiparasitic agent nitazoxanide has shown efficacy against a large number of diarrhea-causing parasites. 
Other infectious agents, like parasites or bacterial toxins, might exacerbate symptoms.  In sanitary living conditions where there's ample food and a supply of clean water, an otherwise healthy person most of the time recovers from viral infections in a few days. Notwithstanding for ill or malnourished individuals, diarrhoea can lead to severe dehydration and can become life-threatening. 
- enzyme deficiencies or mucosal abnormality , as in food allergy and food intolerance, e.g. celiac disease (gluten intolerance), lactose intolerance (intolerance to milk sugar, common in non-Europeans), and fructose malabsorption.
- pernicious anemia , or impaired bowel function due to the inability to absorb vitamin B 12 ,
- loss of pancreatic secretions , which might be due to cystic fibrosis or pancreatitis,
- structural defects , like short bowel syndrome (surgically removed bowel) and radiation fibrosis, like most of the time follows cancer treatment and additional drugs, including agents used in chemotherapy ; and
- certain drugs , like orlistat, which inhibits the absorption of fat.
Inflammatory bowel disease
The two overlapping types here are of unknown origin:
- Ulcerative colitis is marked by chronic bloody diarrhoea and inflammation mostly affects the distal colon near the rectum.
- Crohn's disease typically affects fairly well demarcated segments of bowel in the colon and most often affects the end of the small bowel.
Irritable bowel syndrome
Another possible cause of diarrhoea is irritable bowel syndrome (IBS), which most of the time presents with abdominal discomfort relieved by defecation and unusual stool (diarrhea or constipation) for at least 3 days a week over the previous 3 months.  Symptoms of diarrhea-predominant IBS can be managed through a combination of dietary changes, soluble fibre supplements, and/or medications like loperamide or codeine. About thirty percent of patients with diarrhea-predominant IBS have bile acid malabsorption diagnosed with an abnormal SeHCAT test. 
Diarrhea can be caused by additional diseases and conditions, namely:
- Chronic ethanol ingestion
- Ischemic bowel disease: This most of the time affects older people and can be due to blocked arteries.
- Microscopic colitis, a type of inflammatory bowel disease where changes are only seen on histological examination of colonic biopsies.
- Bile salt malabsorption ( primary bile acid diarrhea) where excessive bile acids in the colon produce a secretory diarrhea.
- Hormone-secreting tumors: a few hormones (e.g., serotonin) can cause diarrhoea if excreted in excess (usually from a tumor).
- Chronic mild diarrhoea in infants and toddlers might occur with no obvious cause and with no additional ill effects; this condition is called toddler's diarrhea.
- Environmental enteropathy
- Radiation enteropathy following treatment for pelvic and abdominal cancers.
Open defecation is a leading cause of infectious diarrhoea leading to death.
Poverty is a good indicator of the rate of infectious diarrhoea in a population. This association doesn't stem from poverty itself, but rather from the conditions under which impoverished people live. The absence of certain resources compromises the ability of the poor to defend themselves against infectious diarrhea. "Poverty is associated with poor housing, crowding, dirt floors, lack of access to clean water or to sanitary disposal of faecal waste ( sanitation), cohabitation with domestic animals that might carry human pathogens, and a lack of refrigerated storage for food, all of which increase the frequency of diarrhea... Poverty additionally restricts the ability to provide age-appropriate, nutritionally balanced diets or to modify diets when diarrhoea develops so as to mitigate and repair nutrient losses. The impact is exacerbated by the lack of adequate, available, and affordable medical care."
One of the most common causes of infectious diarrhea, is a lack of clean water. Often, improper faecal disposal leads to contamination of groundwater. This can lead to widespread infection among a population, especially in the absence of water filtration or purification. Human faeces contains a variety of potentially harmful human pathogens. 
Proper nutrition is important for health and functioning, including the prevention of infectious diarrhea. It is especially important to young children who don't have a fully developed immune system. Zinc deficiency, a condition most often found in children in developing countries can, even in mild cases, have a significant impact on the development and proper functioning of the human immune system.   Indeed, this relationship between zinc deficiency reduced immune functioning corresponds with an increased severity of infectious diarrhea. Children who have lowered levels of zinc have a greater number of instances of diarrhea, severe diarrhea, and diarrhoea associated with fever.  Similarly, vitamin A deficiency can cause an increase in the severity of diarrheal episodes, however there's a few discrepancy when it comes to the impact of vitamin A deficiency on the rate of disease. While a few argue that a relationship doesn't exist between the rate of disease and vitamin A status, others suggest an increase in the rate associated with deficiency.  Given that estimates suggest 127 million preschool children worldwide are vitamin A deficient, this population has the potential for increased risk of disease contraction. 
According to two researchers, Nesse and Williams, diarrhoea might function as an evolved expulsion defence mechanism. As a result, if it is stopped, there might be a delay in recovery. They cite in support of this argument research published in 1973 that found that treating Shigella with the anti-diarrhea drug (Co-phenotrope, Lomotil) caused people to stay feverish twice as long as those not so treated. The researchers indeed themselves observed that: "Lomotil might be contraindicated in shigellosis. Diarrhea might represent a defence mechanism". 
The following types of diarrhoea might indicate further investigation is needed:
- In infants
- Moderate or severe diarrhoea in young children
- Associated with blood
- Continues for more than two days
- Associated non-cramping abdominal pain, fever, weight loss, etc.
- In travelers
- In food handlers, because of the potential to infect others;
- In institutions like hospitals, child care centers, or geriatric and convalescent homes.
A severity score is used to aid diagnosis in children. 
Numerous studies have shown that improvements in drinking water and sanitation ( WASH) lead to decreased risks of diarrhoea.  Such improvements might include for example use of water filters, provision of high-quality piped water and sewer connections. 
In institutions, communities, and households, interventions that promote hand washing with soap lead to significant reductions in the incidence of diarrhea.  The same applies to preventing open defecation at a community-wide level and providing access to improved sanitation.   This includes use of toilets and implementation of the entire sanitation chain connected to the toilets (collection, transport, disposal or reuse of human excreta).
Basic sanitation techniques can have a profound effect on the transmission of diarrheal disease. The implementation of hand washing using soap and water, for example, has been experimentally shown to reduce the incidence of disease by approximately 42–48%.   Hand washing in developing countries, however, is compromised by poverty as acknowledged by the CDC: "Handwashing is integral to disease prevention in all parts of the world; however, access to soap and water is limited in a number of less developed countries. This lack of access is one of a large number of challenges to proper hygiene in less developed countries." Solutions to this barrier require the implementation of educational programmes that encourage sanitary behaviours. 
Given that water contamination is a major means of transmitting diarrheal disease, efforts to provide clean water supply and improved sanitation have the potential to dramatically cut the rate of disease incidence. In fact, it has been proposed that we might expect an 88 percent reduction in child mortality resulting from diarrheal disease as a result of improved water sanitation and hygiene.   Similarly, a meta-analysis of numerous studies on improving water supply and sanitation shows a 22–27% reduction in disease incidence, and a 21–30% reduction in mortality rate associated with diarrheal disease. 
Chlorine treatment of water, for example, has been shown to reduce both the risk of diarrheal disease, and of contamination of stored water with diarrheal pathogens. 
Immunization against the pathogens that cause diarrheal disease is a viable prevention strategy, however it does require targeting certain pathogens for vaccination. In the case of Rotavirus, which was responsible for around six percent of diarrheal episodes and twenty percent of diarrheal disease deaths in the children of developing countries, use of a Rotavirus vaccine in trials in 1985 yielded a slight (2-3%) decrease in total diarrheal disease incidence, while reducing overall mortality by 6-10%. Similarly, a Cholera vaccine showed a strong reduction in morbidity and mortality, though the overall impact of vaccination was minimal as Cholera isn't one of the major causative pathogens of diarrheal disease.  Since this time, more effective vaccines have been developed that have the potential to save a large number of thousands of lives in developing nations, while reducing the overall cost of treatment, and the costs to society.  
A rotavirus vaccine decrease the rates of diarrhoea in a population.  New vaccines against rotavirus, Shigella , Enterotoxigenic Escherichia coli (ETEC), and cholera are under development, as well as additional causes of infectious diarrhea.
Dietary deficiencies in developing countries can be combated by promoting better eating practices. Supplementation with vitamin A and/or zinc. Zinc supplementation proved successful showing a significant decrease in the incidence of diarrheal disease compared to a control group.   The majority of the literature suggests that vitamin A supplementation is advantageous in reducing disease incidence.  Development of a supplementation strategy should take into consideration the fact that vitamin A supplementation was less effective in reducing diarrhoea incidence when compared to vitamin A and zinc supplementation, and that the latter strategy was estimated to be significantly more cost effective. 
Breastfeeding practises have been shown to have a dramatic effect on the incidence of diarrheal disease in poor populations. Studies across a number of developing nations have shown that those who receive exclusive breastfeeding throughout their first 6 months of life are better protected against infection with diarrheal diseases.  Exclusive breastfeeding is currently recommended during, at least, the first six months of an infant's life by the WHO. 
In a large number of cases of diarrhea, replacing lost fluid and salts is the only treatment needed. This is most of the time by mouth – oral rehydration therapy – or, in severe cases, intravenously.  Diet restrictions like the BRAT diet are no longer recommended.  Research doesn't support the limiting of milk to children as doing so has no effect on duration of diarrhea.  To the contrary, WHO recommends that children with diarrhoea continue to eat as sufficient nutrients are most of the time still absorbed to support continued growth and weight gain, and that continuing to eat additionally speeds up recovery of normal intestinal functioning.  CDC recommends that children and adults with cholera additionally continue to eat. 
Oral rehydration solution (ORS) (a slightly sweetened and salty water) can be used to prevent dehydration. Standard home solutions like salted rice water, salted yoghourt drinks, vegetable and chicken soups with salt can be given. Home solutions like water in which cereal has been cooked, unsalted soup, green coconut water, weak tea (unsweetened), and unsweetened fresh fruit juices can have from half a teaspoon to full teaspoon of salt (from one-and-a-half to three grams) added per liter. Clean plain water can additionally be one of several fluids given.  There are commercial solutions like Pedialyte, and relief agencies like UNICEF widely distribute packets of salts and sugar. A WHO publication for physicians recommends a homemade ORS consisting of one litre water with one teaspoon salt (3 grams) and two tablespoons sugar (18 grams) added  (approximately the "taste of tears"  ). Rehydration Project recommends adding the same amount of sugar but only one-half a teaspoon of salt, stating that this more dilute approach is less risky with quite little loss of effectiveness.  Both agree that drinks with too much sugar or salt can make dehydration worse.  
Appropriate amounts of supplemental zinc and potassium should be added if available. But the availability of these shouldn't delay rehydration. As WHO points out, the most important thing is to start preventing dehydration as early as possible.  In another example of prompt ORS hopefully preventing dehydration, CDC recommends for the treatment of cholera continuing to give Oral Rehydration Solution throughout travel to medical treatment. 
Vomiting most often occurs throughout the first hour or two of treatment with ORS, especially if a child drinks the solution too quickly, but this seldom prevents successful rehydration after most of the fluid is still absorbed. WHO recommends that if a child vomits, to wait five or ten minutes and then start to give the solution again more slowly. 
Drinks especially high in simple sugars, like soft drinks and fruit juices, aren't recommended in children under 5 years of age as they might increase dehydration. A too rich solution in the gut draws water from the rest of the body, just as if the person were to drink sea water.   Plain water might be used if more specific and effective ORT preparations are unavailable or aren't palatable.  Additionally, a mix of both plain water and drinks perhaps too rich in sugar and salt can alternatively be given to the same person, with the goal of providing a medium amount of sodium overall.  A nasogastric tube can be used in young children to administer fluids if warranted. 
WHO recommends a child with diarrhoea continue to be fed. Continued feeding speeds the recovery of normal intestinal function. In contrast, children whose food is restricted have diarrhoea of longer duration and recover intestinal function more slowly. A child should additionally continue to be breastfed. The WHO states "Food should never be withheld and the child's usual foods should not be diluted. Breastfeeding should always be continued."  And in the specific example of cholera, CDC additionally makes the same recommendation.  In young children who aren't breast-fed and live in the developed world, a lactose-free diet might be useful to speed recovery. 
While antibiotics are beneficial in certain types of acute diarrhea, they're most of the time not used except in specific situations.   There are concerns that antibiotics might increase the risk of hemolytic uremic syndrome in people infected with Escherichia coli O157:H7.  In resource-poor countries, treatment with antibiotics might be beneficial.  Notwithstanding a few bacteria are developing antibiotic resistance, particularly Shigella .  Antibiotics can additionally cause diarrhea, and antibiotic-associated diarrhea is the most common adverse effect of treatment with general antibiotics.
While bismuth compounds ( Pepto-Bismol) decreased the number of bowel movements in those with travelers' diarrhea, they don't decrease the length of illness.  Anti-motility agents like loperamide are additionally effective at reducing the number of stools but not the duration of disease.  These agents should only be used if bloody diarrhoea isn't present. 
Bile acid sequestrants like cholestyramine can be effective in chronic diarrhoea due to bile acid malabsorption. Therapeutic trials of these drugs are indicated in chronic diarrhoea if bile acid malabsorption can't be diagnosed with a specific test, like SeHCAT retention.
Zinc supplementation benefits children with diarrhoea in developing countries, but only in infants over six months old. This supports the World Health Organization guidelines for zinc, but not in the quite young. 
Probiotics reduce the duration of symptoms by one day and reduced the chances of symptoms lasting longer than four days by 60%.  The probiotic lactobacillus can help prevent antibiotic-associated diarrhea in adults but possibly not children.  For those with lactose intolerance, taking digestive enzymes containing lactase when consuming dairy products most often improves symptoms.
Worldwide in 2004, approximately 2.5 billion cases of diarrhoea occurred, which resulted in 1.5 million deaths among children under the age of five.  Greater than half of these were in Africa and South Asia.  This is down from a death rate of 4.5 million in 1980 for gastroenteritis.  Diarrhea remains the second leading cause of infant mortality (16%) after pneumonia (17%) in this age group. 
The majority of such cases occur in the developing world, with over half of the recorded cases of childhood diarrhoea occurring in Africa and Asia, with 696 million and 1.2 billion cases, respectively, compared to only 480 million in the rest of the world.
Infectious diarrhoea resulted in about 0.7 million deaths in children under five years old in 2011 and 250 million lost school days.   In the Americas, diarrheal disease accounts for a total of ten percent of deaths among children aged 1–59 months while in South East Asia, it accounts for 31.3% of deaths.  It is estimated that around twenty-one percent of child mortalities in developing countries are due to diarrheal disease.