An electron micrograph of rotavirus, the cause of nearly 40% of hospitalizations from diarrhea in children under five
Bristol stool chart
Diagram of the human gastrointestinal tract
Poverty often leads to unhygienic living conditions, as in this community in the Indian Himalayas. Such conditions promote contraction of diarrheal diseases, as a result of poor sanitation and hygiene.
A person consuming oral rehydration solution
Deaths due to diarrhoeal diseases per million persons in 2012

Condition of having at least three loose, liquid, or watery bowel movements each day.

- Diarrhea

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Lactose intolerance

Common condition caused by a decreased ability to digest lactose, a sugar found in dairy products.

Lactose is made up of two simple sugars
Rough rates of lactose intolerance in different regions of the world
An estimate of the percentage of adults that can digest lactose in the indigenous population of the Old World

Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea.

Irritable bowel syndrome

Functional gastrointestinal disorder characterized by a group of symptoms accompanied together that include abdominal pain and changes in the consistency of bowel movements.

Drawing of the pain of IBS
Prevalence of protozoal infections in industrialized countries (United States and Canada) in the 21st century
Percentage of population with IBS reported in various studies in different countries (see sources in the table)

It has been classified into four main types depending on whether diarrhea is common, constipation is common, both are common (mixed/alternating), or neither occurs very often (IBS-D, IBS-C, IBS-M/IBS-A, or IBS-U, respectively).


Necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus.

Human anatomy of the anorecturm (anus and rectum)
The caganer is a defecating figurine in Spanish nativity scenes

There are a number of medical conditions associated with defecation, such as diarrhea and constipation, some of which can be serious.

Coeliac disease

Long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barley.

Biopsy of small bowel showing coeliac disease manifested by blunting of villi, crypt hypertrophy, and lymphocyte infiltration of crypts
DQ α5-β2 -binding cleft with a deamidated gliadin peptide (yellow), modified from
HLA region of chromosome 6
Illustration of deamidated α-2 gliadin's 33mer, amino acids 56–88, showing the overlapping of three varieties of T-cell epitope
The active form of tissue transglutaminase (green) bound to a gluten peptide mimic (blue).
Immunofluorescence staining pattern of endomysial antibodies on a monkey oesophagus tissue sample.
Endoscopic still of duodenum of a person with coeliac disease showing scalloping of folds and "cracked-mud" appearance to mucosa
Schematic of the Marsh classification of upper jejunal pathology in coeliac disease.

Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite, and among children failure to grow normally.


Condition that occurs due to excessive production of thyroid hormones by the thyroid gland.

Triiodothyronine (T3, pictured) and thyroxine (T4) are both forms of thyroid hormone.
Illustration depicting enlarged thyroid that may be associated with hyperthyroidism
Most common causes of hyperthyroidism by age.

Signs and symptoms vary between people and may include irritability, muscle weakness, sleeping problems, a fast heartbeat, heat intolerance, diarrhea, enlargement of the thyroid, hand tremor, and weight loss.

Ulcerative colitis

Long-term condition that results in inflammation and ulcers of the colon and rectum.

Endoscopic image of a colon affected by ulcerative colitis. The internal surface of the colon is blotchy and broken in places. Mild-moderate disease.
Classification of colitis, often used in defining the extent of involvement of ulcerative colitis, with proctitis (blue), proctosigmoiditis (yellow), left sided colitis (orange) and pancolitis (red). All classes extend distally to the end of the rectum.
Gross pathology of normal colon (left) and severe ulcerative colitis (right), forming pseudopolyps (smaller than the cobblestoning typically seen in Crohn's disease), over a continuous area (rather than skip lesions of Crohn's disease), and with a relatively gradual transition from normal colon (while Crohn's is typically more abrupt).
Aphthous ulcers involving the tongue, lips, palate, and pharynx.
Pyoderma gangrenosum with large ulcerations affecting the back.
Endoscopic image of ulcerative colitis affecting the left side of the colon. The image shows confluent superficial ulceration and loss of mucosal architecture. Crohn's disease may be similar in appearance, a fact that can make diagnosing UC a challenge.
H&E stain of a colonic biopsy showing a crypt abscess, a classic finding in ulcerative colitis
Colonic pseudopolyps of a person with intractable UC, colectomy specimen
Biopsy sample (H&E stain) that demonstrates marked lymphocytic infiltration (blue/purple) of the intestinal mucosa and architectural distortion of the crypts.

The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood.

Inflammatory bowel disease

Group of inflammatory conditions of the colon and small intestine, Crohn's disease and ulcerative colitis being the principal types.

Micrograph showing inflammation of the large bowel in a case of inflammatory bowel disease. Colonic biopsy. H&E stain.
Associated loci pane. Pink genes are in IBD associated loci, blue are not.

In spite of Crohn's and UC being very different diseases, both may present with any of the following symptoms: abdominal pain, diarrhea, rectal bleeding, severe internal cramps/muscle spasms in the region of the pelvis and weight loss.


Lack of total body water, with an accompanying disruption of metabolic processes.

Nurses encourage a patient to drink an oral rehydration solution to treat the combination of dehydration and hypovolemia secondary to cholera. Cholera leads to GI loss of both excess free water (dehydration) and sodium (hence ECF volume depletion—hypovolemia).
Urine color as an indicator of hydration

Excess free water or hypotonic water can leave the body in two ways – sensible loss such as osmotic diuresis, sweating, vomiting and diarrhea, and insensible water loss, occurring mainly through the skin and respiratory tract.


Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage.

The sanitation system: collection, transport, treatment, disposal or reuse.
Urban improved sanitation facilities versus rural improved sanitation facilities, 2015.
Access to safe drinking water and sanitation (2016)
Percentage of population served by different types of sanitation systems
Example of sanitation infrastructure: Shower, double-vault urine-diverting dry toilet (UDDT) and waterless urinal in Lima, Peru
Emergency pit lining kits by Evenproducts
Share of population using safely managed sanitation facilities in 2015
Number of Handwashing Facilities in the world, 2017
Sewage treatment plant, Australia.
Hiriya Landfill, Israel.
Modern restaurant food preparation area.
Hygiene education (on proper handwashing) in Afghanistan
The "F-diagram" (feces, fingers, flies, fields, fluids, food), showing pathways of fecal-oral disease transmission. The vertical blue lines show barriers: toilets, safe water, hygiene and handwashing.
United Nations SDG 6 Logo
Example for lack of sanitation: Unhygienic pit latrine with ring slab in Kalibari community in Mymensingh, Bangladesh
Modified logo of International Year of Sanitation, used in the UN Drive to 2015 campaign logo

For example, diarrhea, a main cause of malnutrition and stunted growth in children, can be reduced through adequate sanitation.

Infant mortality

Death of young children under the age of 1.

World map of infant mortality rates in 2017
Infant mortality rates are higher in countries with higher economic inequality
Countries by 2019 GDP (nominal) per capita.
Map of countries by fertility rate (2020), according to the Population Reference Bureau
Infant mortality rate by region
Life expectancy at birth by region
1906 headline imploring parents to attend to the cleanliness of their infants, and to expose them to the "clean air" outdoors.
Data indicating the IMR disparity between infants Non-Hispanic black mothers and infants of white or Hispanic mothers in the United States from 2000 to 2010.
This 1860 woodcut by Julius Schnorr von Karolsfeld depicts the death of Bathsheba's first child with David, who lamented, "I shall go to him, but he will not return to me"

Other leading causes of infant mortality include birth asphyxia, pneumonia, congenital malformations, term birth complications such as abnormal presentation of the fetus umbilical cord prolapse, or prolonged labor, neonatal infection, diarrhea, malaria, measles and malnutrition.