It is often associated with alcoholism and eating disorders and there is some evidence that presence of a hiatal hernia is a predisposing condition. Forceful vomiting causes tearing of the mucosa at the junction. NSAID abuse is also a rare association.

The tear involves the mucosa and submucosa but not the muscular layer (contrast to Boerhaave syndrome which involves all the layers). The mean age is more than 60 and 80% are men.

Hyperemesis gravidarum, which is severe morning sickness associated with vomiting and retching in pregnancy, is also a known cause of Mallory-Weiss tear.

Mallory–Weiss syndrome or gastro-esophageal laceration syndrome refers to bleeding from a laceration in the mucosa at the junction of the stomach and esophagus. This is usually caused by severe vomiting because of alcoholism or bulimia, but can be caused by any conditions which causes violent vomiting and retching such as food poisoning. The syndrome presents with hematemesis. The laceration is sometimes referred to as a "Mallory-Weiss tear".

With the exception of a few case reports describing survival without surgery, the mortality of untreated Boerhaave syndrome is nearly 100%. Its treatment includes immediate antibiotic therapy to prevent mediastinitis and sepsis, surgical repair of the perforation, and if there is significant fluid loss it should be replaced with IV fluid therapy since oral rehydration is not possible. Even with early surgical intervention (within 24 hours) the risk of death is 25%.

Esophageal rupture in Boerhaave syndrome is thought to be the result of a sudden rise in internal esophageal pressure produced during vomiting, as a result of neuromuscular incoordination causing failure of the cricopharyngeus muscle (a sphincter within the esophagus) to relax. As the intra-oesophageal pressure increases, the bolus within the oesophagus has nowhere to go superiorly (as the cricopharyngeus fails to relax) which causes the oesophagus to rupture. (this makes little sense and should be justified if true: the lesion is down, the cricopharyngeus is up). The syndrome is commonly associated with the consumption of excessive food and/or alcohol as well as eating disorders such as bulimia.

The most common anatomical location of the tear in Boerhaave syndrome is at left posterolateral wall of the lower third of the esophagus, 2–3 cm before the stomach.

Currently, the most common cause of esophageal perforation is iatrogenic. However, iatrogenic perforations, while still constituting a serious medical condition, are easier to treat and less prone to complications, particularly mediastinitis and sepsis. This is because they usually do not involve contamination of the mediastinum with gastric contents.

The effects of HG on the fetus are mainly due to electrolyte imbalances caused by HG in the mother. Infants of women with severe hyperemesis who gain less than 7 kg (15.4 lb) during pregnancy tend to be of lower birth weight, small for gestational age, and born before 37 weeks gestation. In contrast, infants of women with hyperemesis who have a pregnancy weight gain of more than 7 kg appear similar to infants from uncomplicated pregnancies. There is no significant difference in the neonatal death rate in infants born to mothers with HG compared to infants born to mothers who do not have HG. Children born to mothers with undertreated Hyperemesis have a fourfold increase in neurobehavioral diagnoses.

Vomiting is a common condition affecting about 50% of pregnant women, with another 25% having nausea. However, the incidence of HG is only 0.3–1.5%. After preterm labor, hyperemesis gravidarum is the second most common reason for hospital admission during the first half of pregnancy. Factors such as infection with "Helicobacter pylori", a rise in thyroid hormone production, low age, low body mass index prior to pregnancy, multiple pregnancies, molar pregnancies, and a past history of hyperemesis gravidarum have been associated with the development of HG.

Causes can be:

- Mallory-Weiss syndrome: bleeding tears in the esophagal mucosa, usually caused by prolonged and vigorous retching.

- Irritation or erosion of the lining of the esophagus or stomach

- Vomiting of ingested blood after hemorrhage in the oral cavity, nose or throat

- Vascular malfunctions of the gastrointestinal tract, such as bleeding gastric varices or intestinal varices

- Tumors of the stomach or esophagus.

- Radiation poisoning

- Viral hemorrhagic fevers

- Gastroenteritis

- Gastritis

- Peptic ulcer

- Chronic viral hepatitis

- Intestinal schistosomiasis (caused by the parasite "Schistosoma mansoni")

- History of smoking

- Iatrogenic injury (invasive procedure such as endoscopy or transesophageal echocardiography)

- Zollinger–Ellison syndrome (severe peptic ulcer)

- Atrio-oesophageal fistula

- Yellow fever

Esophageal diseases can derive from congenital conditions, or they can be acquired later in life.

Many people experience a burning sensation in their chest occasionally, caused by stomach acids refluxing into the esophagus, normally called heartburn. Extended exposure to heartburn may erode the lining of the esophagus, leading potentially to Barrett's esophagus which is associated with an increased risk of adenocarcinoma most commonly found in the distal one-third of the esophagus.

Some people also experience a sensation known as globus esophagus, where it feels as if a ball is lodged in the lower part of the esophagus.

The following are additional diseases and conditions that affect the esophagus:

- Achalasia

- Acute esophageal necrosis

- Barrett's esophagus

- Boerhaave syndrome

- Caustic injury to the esophagus

- Chagas disease

- Diffuse esophageal spasm

- Esophageal atresia and Tracheoesophageal fistula

- Esophageal cancer

- Esophageal dysphagia

- Esophageal varices

- Esophageal web

- Esophagitis

- GERD

- Hiatus hernia

- Jackhammer esophagus (hypercontractile peristalsis)

- Killian–Jamieson diverticulum

- Mallory-Weiss syndrome

- Neurogenic dysphagia

- Nutcracker esophagus

- Schatzki's ring

- Zenker's Diverticulum

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. Heightened mast cell activation has been proposed to be a common factor among FGIDs, contributing to visceral hypersensitivity as well as epithelial, neuromuscular, and motility dysfunction.

Hematemesis or haematemesis is the vomiting of blood. The source is generally the upper gastrointestinal tract, typically above the suspensory muscle of duodenum. Patients can easily confuse it with hemoptysis (coughing up blood), although the latter is more common. Hematemesis "is always an important sign".

Oesophageal diseases include a spectrum of disorders affecting the oesophagus. The most common condition of the oesophagus in Western countries is gastroesophageal reflux disease, which in chronic forms is thought to result in changes to the epithelium of the oesophagus, known as Barrett's oesophagus.

Acute disease might include infections such as oesophagitis, trauma caused ingestion of corrosive substances, or rupture of veins such as oesophageal varices, Boerhaave syndrome or Mallory-Weiss tears. Chronic diseases might include congenital diseases such as Zenker's diverticulum and esophageal webbing, and oesophageal motility disorders including the nutcracker oesophagus, achalasia, diffuse oesophageal spasm, and oesophageal stricture.

Oesophageal disease may result in a sore throat, throwing up blood, difficulty swallowing or vomiting. Chronic or congenital diseases might be investigated using barium swallows, endoscopy and biopsy, whereas acute diseases such as reflux may be investigated and diagnosed based on symptoms and a medical history alone.

Respiratory complications are often cause of death in early infancy.

Diseases of the hepatobiliary system affect the biliary tract (also known as the "biliary tree"), which secretes bile in order to aid digestion of fats. Diseases of the gallbladder and bile ducts are commonly diet-related, and may include the formation of gallstones that impact in the gallbladder (cholecystolithiasis) or in the common bile duct (choledocholithiasis).

Gallstones are a common cause of inflammation of the gallbladder, called cholecystitis. Inflammation of the biliary duct is called cholangitis, which may be associated with autoimmune disease, such as primary sclerosing cholangitis, or a result of bacterial infection, such as ascending cholangitis.

Disease of the biliary tree may cause pain in the upper right abdomen, particularly when pressed. Disease might be investigated using ultrasound or ERCP, and might be treated with drugs such as antibiotics or UDCA, or by the surgical removal of the gallbladder.

The first gene that could cause the syndrome is described recently and is called NF1X (chromosome 19: 19p13.1).

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

In the United States, sarcoidosis has a prevalence of approximately 10 cases per 100,000 whites and 36 cases per 100,000 blacks. Heerfordt syndrome is present in 4.1–5.6% of those with sarcoidosis.

In most cases Ballantyne syndrome causes fetal or neonatal death and in contrast, maternal involvement is limited at the most to preeclampsia.

In terms of epidemiology, Jackson–Weiss syndrome is a rare genetic disorder; the overall contribution of FGFR mutation to the condition is not clear.

Although the exact etiopathogenetic mechanism of Ballantyne syndrome remains unknown, several authors have reported raised uric acid levels, anemia, and low hematocrit without hemolysis.

Chvostek's sign is found in tetany.

It may also be present in hypomagnesemia, Magnesium is a cofactor for Adenylate cyclase. The reaction that Adenylate cyclase catalyzes is the conversion of ATP to 3',5'-cyclic AMP. The 3',5'-cyclic AMP (cAMP) is required for parathyroid hormone activation. It is frequently seen in alcoholics, persons with diarrhea, patients taking aminoglycosides or diuretics, because hypomagnesemia can cause hypocalcemia. It is also seen in measles, tetanus and myxedema.

It can also be found in subjects with respiratory alkalosis, for example as a result of hyperventilation syndrome, which can lead to a drastic reduction of the concentration in serum of calcium ions while at normal levels, for the binding of a significant proportion of ionized calcium (Ca 2+ ) with albumin and globulins.

Roberts syndrome is an extremely rare condition that only affects about 150 reported individuals. Although there have been only about 150 reported cases, the affected group is quite diverse and spread worldwide. Parental consanguinity (parents are closely related) is common with this genetic disorder. The frequency of Roberts syndrome carriers is unknown.

It is likely that this syndrome is inherited in an autosomal dominant fashion, however there may be a recessive form with hypotonia and developmental delay.

Scalp–ear–nipple syndrome (also known as "Finlay–Marks syndrome") is a condition associated with aplasia cutis congenita.

Webbed toes in humans are a purely cosmetic condition. This condition does not impair the ability to perform any activity, including walking, running, or swimming. Depending on the severity and structure of the webbing, there can be some minor consequences.

People with more severe webbed toes may have a slight disadvantage for activities that benefit from prehensile toes, due to the toes being unable to split or move laterally. Although not scientifically proven, some believe that this condition can possibly allow for a slight advantage, specifically, in athletics. Considering your big toe is a main source for balance, having your second and third toe webbed could virtually be seen as having two big toes. Thus, allowing for better balance in athletics such as running or dance.

Psychological stress may arise from the fear of negative reactions to this condition from people who do not have webbed toes, particularly in severe cases where the nails are stuck visibly close together. Many people with webbed toes can physically feel the toes touching under the fused skin, which can cause psychological discomfort. This is due to the nerves of each toe fully developing and independent muscles working. In other cases where the toes are partially webbed, the webbing holds the separate tips of the toes against one another and prevents the muscles from spreading the toes apart, causing the toes and sometimes nails to press together.

However a disadvantage would be a difficulty in wearing flip-flops or other such footwear in warm countries. People with webbed toes may be unable to wear Toe socks or Vibram FiveFingers shoes. Difficulty navigating rough terrain barefoot, such as rocks at a beach is also common. In some cases the toes grow at different lengths causing the toes to buckle or bend and many people with severe webbed toes experience cramping in these toes due to the muscles and ligaments being strained.

The exact cause of the condition is unknown. In some cases, close family members may share this condition. In other cases, no other related persons have this condition. The scientific name for the condition is syndactyly, although this term covers both webbed fingers and webbed toes. Syndactyly occurs when apoptosis or programmed cell death during gestation is absent or incomplete. Webbed toes occur most commonly in the following circumstances:

- Syndactyly or Familial Syndactyly

- Down syndrome

It is also associated with a number of rare conditions, notably:

- Aarskog–Scott syndrome

- Acrocallosal syndrome

- Apert's syndrome

- Bardet-Biedl syndrome

- Carpenter syndrome

- Cornelia de Lange syndrome

- Edwards syndrome

- Jackson–Weiss syndrome

- Fetal hydantoin syndrome

- Miller syndrome

- Pfeiffer syndrome

- Smith-Lemli-Opitz syndrome

- Timothy syndrome

- Ectodermal Dysplasia

- Klippel-Feil Syndrome