Diarrhea happens when the amount of fluids absorbed in the intestine does not match the amount secreted. The imbalance can be achieved in two ways: an excess of secretion or a lack of absorption. Thus, diarrhea can be categorized into secretory diarrhea, an excess of secretion, or osmotic diarrhea which is a lack of absorption. Usually both categories are present in<unk>  diarrhea of infants. Secretory diarrhea can be caused by either infectious or non-infectious agents. Infectious agents include bacteria, viruses, and protozoans while non-infectious agents can be hormones, neurotransmitters, cytokines, and others. Osmotic diarrhea occurs when nutrients that are not absorbed exists in the intestines, typically due to damage to the intestines. The nutrients that are unable to be absorbed in the intestines draws water to itself. Some factors that lead to<unk> : * Underdeveloped digestive system, nutrients do not spend adequate time in the digestive tract for water to be absorbed which leads to diarrhea. * Imbalanced Diet - a diet that has excess fiber and/or a lack of fat, fat can slow down the digestion process and prolong the amount of time nutrients spend in the tract which increases absorption. Fiber can lead to diarrhea because it shortens the amount of time food spends in the intestines, decreasing absorption. * Inability to absorb carbohydrates The specific source of<unk>  diarrhea typically depends on the age of the infant/child. Diarrhea is uncommon for newborns; consequently, its presence in newborns could indicate a congenital disorder which would need hospitalization. Rare causes of<unk>  diarrhea in young children include a group of genetic mutations known as "congenital diarrhea and enteropathies" (CODEs). This group of genetic disorders usually presents in the first weeks of birth as severe and debilitating diarrhea and can lead to malabsorption, growth failure, and difficulty feeding. CODEs are rare genetic changes to a single gene that affects the lining of the intestine or changes to the immune system that also affects the cell function of important nutrient and electrolyte transporters in the intestine such as Cl−/HCO3− mutation. Otherwise, socioeconomic factors and access to treatment/healthcare play a significant part in developing<unk>  diarrhea as an infant. For instance, leading causes of<unk>  diarrhea in developing countries are infections of the intestine. In developed countries,<unk>  diarrhea has a diverse range of causes such as<unk>  infection of the intestines, autoimmune enteropathy, and inability to absorb nutrients via celiac disease, food sensitivities, etc. From age 0–30 days, typical causes are: * Abetalipoproteinemia, a condition caused by a genetic mutation that creates abnormal absorption of fats and some vitamins. * Acrodermatitis enteropathica, a condition in which the intestine cannot absorb zinc. * Autoimmune enteropathy, a rare condition in which the intestines are perceived as a foreign threat by the immune system and are attacked leading to irritation and inflammation. * Microvillous inclusion disease, a condition caused by a genetic mutation leading to severe diarrhea because intestinal cells did not have normal development and thus the intestines are not able to absorb nutrients properly. * Congenital chloride diarrhea, a lifelong condition caused by a genetic mutation that leads to diarrhea with a high concentration of chloride. * Congenital sodium diarrhea, a genetic disorder caused by mutations in electrolyte transporters that disrupt the transport of Na+ across the intestine and results in high levels of Na+ greater than 145 mM in the stool. * Congenital short-bowel syndrome, a condition in which a portion of the small intestine is absent or not functioning properly leading to decreased absorption of both fluids and nutrients. * Congenital lactase deficiency, a condition caused by a genetic mutation in which the body cannot digest lactose properly. * Glucose-galactose malabsorption, a genetic disorder caused by changes in a protein critical for the transport of glucose and galactose across the intestine which leads to impaired glucose/galactose absorption, dehydration, and severe diarrhea in young children. Typically, the severe diarrhea improves with a diet low in glucose/galactose and the tolerability to glucose/galactose improves with age. * Hirschsprung's disease (HSCR), a gut motility disorder characterized by a lack of nerve cells in the large intestine which are needed to move the stool through the digestive tract. In infants, HSCR typically presents when a newborn is unable to pass the first feces, or meconium within 48 hours of birth. Other symptoms include blockage of the intestine, fever, rapid release of stool and flatulence upon rectal examination, and may present with diarrhea in infants. * Intestinal pseudo-obstruction (IPO), a gut motility disorder characterized by the inability to contract intestinal walls with symptoms similar to intestinal obstruction but lack a distinguishable cause of obstruction. Signs and symptoms include abdominal pain, dilated or enlarged bowel, constipation and may include diarrhea. Although rare in infants, IPO is a type of congenital disorder that may present with diarrhea in infants. * Primary bile acid malabsorption, a gut defect in the reabsorption of bile acids in the small intestine which results in increased levels of bile acids in the colon leading to watery diarrhea and bloating. *<unk>  infection of C. difficile, G. lamblia * C. difficile - bacteria that can be the source of diarrhea. * G. lamblia - a parasite that can be the source diarrhea. From 1–12 months, typical causes of<unk>  diarrhea are the following: * Acrodermatitis enteropathica, a condition in which the intestine cannot absorb zinc. * Cystic fibrosis, a condition caused by a genetic mutation that can lead to injury to the body's organs including the lungs and those in the digestive system. * Apple juice and pear nectar, the digestive tract of children have difficulty absorbing significant quantities of sugars and carbohydrates which certain fruit juices can have. * Celiac Disease, a disorder in which there is an immune response to eating gluten which can eventually cause damage to the small intestine over time and impedes absorption. * Food allergy. Most instances of<unk>  diarrhea in<unk>  are caused by infectious and post infectious disease of the intestine as well as food sensitivities or allergies.
Chronic diarrhea of infancy
Milk allergy
Food protein-induced enterocolitis syndrome
Wilderness-acquired diarrhea
Brainerd diarrhea
Neutropenic enterocolitis
Congenital tufting enteropathy
Necrotizing enterocolitis