Diarrhoea is the passage of unusually loose, watery or frequent stools and is a symptom rather than a single disease. Acute Diarrhoea commonly develops over a short period and is frequently associated with infections, contaminated food or water, medication effects or dietary factors. Persistent or chronic diarrhoea has a different differential diagnosis and can arise from inflammatory, malabsorptive, secretory, functional, endocrine or structural disorders. Clinically, the amount of stool water and the resulting loss of fluid and electrolytes are more important than frequency alone. The major immediate danger of significant acute diarrhoea is dehydration, particularly in infants, older adults and people with other illnesses.
Intestinal Diarrhoea can arise through several physiological mechanisms. Osmotic diarrhoea occurs when poorly absorbed substances retain water within the intestinal lumen, whereas secretory diarrhoea results from increased secretion or reduced absorption of electrolytes and water. Inflammatory diarrhoea can result from mucosal injury and may contain blood, mucus or inflammatory cells. Rapid intestinal transit can also reduce the time available for water absorption. Infectious organisms can produce diarrhoea through combinations of toxin production, mucosal invasion, inflammation and altered secretion. These mechanisms can overlap, so clinical presentation alone does not always identify the precise physiological cause.
Acute Diarrhoea is frequently caused by infectious gastroenteritis involving viruses, bacteria or parasites. Other causes include antibiotic-associated changes in intestinal flora, adverse drug reactions, excessive alcohol intake, food intolerances and sudden dietary changes. Chronic diarrhoea can occur with inflammatory bowel disease, coeliac disease, pancreatic insufficiency, bile-acid malabsorption, microscopic colitis, some endocrine disorders and functional gastrointestinal conditions. Certain medicines, including some antibiotics, metformin and laxatives, can produce diarrhoea. A careful history covering travel, food exposure, medicines, duration, stool characteristics and associated symptoms can substantially narrow the possibilities.
The principal treatment priority in acute Diarrhoea is replacement of lost fluid and electrolytes. Oral rehydration solutions contain appropriate concentrations of water, sodium, glucose and other electrolytes that facilitate intestinal absorption and are more effective than many ordinary drinks for significant dehydration. Severe dehydration may require intravenous fluids. Food intake does not necessarily need to stop completely, and appropriate nutrition can generally be resumed as tolerated. Antibiotics are not routinely required because many infectious episodes are viral or self-limiting, and inappropriate antimicrobial use can cause adverse effects and contribute to antimicrobial resistance. Treatment should therefore be directed at the cause and severity rather than at the symptom alone.
Diarrhoea can be particularly dangerous when fluid loss exceeds the body's ability to replace it. Signs of dehydration can include thirst, dry mouth, reduced urination, dizziness, weakness and, in severe cases, confusion or circulatory collapse. Infants and young children can deteriorate rapidly because they have smaller fluid reserves, while older adults and people with kidney or cardiovascular disease may have additional risks. Blood in the stool, high fever, severe abdominal pain, persistent vomiting, marked weakness, prolonged symptoms or signs of significant dehydration warrant medical assessment. Recent hospitalisation or antibiotic exposure can also be important because particular infections can follow disruption of the intestinal microbiome.
Diagnosis depends strongly on duration and clinical context. Short-lived uncomplicated Diarrhoea often does not require laboratory testing, whereas persistent, severe or bloody diarrhoea may warrant stool studies, blood tests, imaging or endoscopic assessment. Testing can identify particular pathogens, inflammatory processes or malabsorptive conditions when the result would alter management. Chronic diarrhoea requires consideration of the relationship between symptoms and food, medication, bowel movements, weight changes and systemic manifestations. Distinguishing diarrhoea caused by increased stool water from frequent passage of normally formed stool is also important because the latter can result from altered bowel habits without true diarrhoea.
Prevention of infectious Diarrhoea depends substantially on safe water, sanitation, hand hygiene, food hygiene and appropriate management of contaminated environments. Food should be stored, prepared and cooked appropriately, and cross-contamination between raw and ready-to-eat foods should be avoided. Vaccination can prevent particular diarrhoeal infections in relevant populations, while antimicrobial stewardship reduces unnecessary disruption of intestinal flora. During an outbreak, infection-control measures can reduce transmission. Public-health surveillance also uses diarrhoeal disease patterns to identify contaminated water, foodborne outbreaks and emerging infectious threats.
Diarrhoea should be distinguished from conditions such as faecal urgency, faecal incontinence and frequent bowel movements with normal stool consistency. It can coexist with nausea, vomiting, abdominal cramps and fever, particularly in infectious gastroenteritis, but the combination does not establish a specific cause. Acute Diarrhoea often resolves spontaneously, whereas persistent or recurrent symptoms require consideration of non-infectious causes. The term therefore describes a physiological symptom pattern that ranges from a brief, self-limiting disturbance to a manifestation of serious intestinal or systemic disease, and interpretation depends on duration, severity, stool characteristics, associated symptoms and the person's clinical context.
