Bloating in the context of "Small intestinal bacterial overgrowth"

Lactose intolerance is caused by a lessened ability or a complete inability to digest lactose, a sugar found in dairy products. Humans vary in the amount of lactose they can tolerate before symptoms develop. Symptoms may include abdominal pain, bloating, diarrhea, flatulence, and nausea. These symptoms typically start thirty minutes to two hours after eating or drinking something containing lactose, with the severity typically depending on the amount consumed. Lactose intolerance does not cause damage to the gastrointestinal tract.

Lactose intolerance is due to the lack of the enzyme lactase in the small intestines to break lactose down into glucose and galactose. There are four types: primary, secondary, developmental, and congenital. Primary lactose intolerance occurs as the amount of lactase declines as people grow up. Secondary lactose intolerance is due to injury to the small intestine. Such injury could be the result of infection, celiac disease, inflammatory bowel disease, or other diseases. Developmental lactose intolerance may occur in premature babies and usually improves over a short period of time. Congenital lactose intolerance is an extremely rare genetic disorder in which little or no lactase is made from birth. The reduction of lactase production starts typically in late childhood or early adulthood, but prevalence increases with age.

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may occur over a long time, sometimes for years. IBS can negatively affect quality of life and may result in missed school or work or reduced productivity at work. Disorders such as anxiety, major depression, and myalgic encephalomyelitis/chronic fatigue syndrome are common among people with IBS, sometimes developing due to the condition.

The cause of IBS is not known but multiple factors have been proposed to lead to the condition. Theories include combinations of "gut–brain axis" problems, alterations in gut motility, visceral hypersensitivity, infections including small intestinal bacterial overgrowth, neurotransmitters, genetic factors, and food sensitivity. Onset may be triggered by a stressful life event, or an intestinal infection. In the latter case, it is called post-infectious irritable bowel syndrome.

Premenstrual syndrome (PMS) is a disruptive set of emotional and physical symptoms that regularly occur in the one to two weeks before the start of each menstrual period. Symptoms resolve around the time menstrual bleeding begins. Symptoms vary, though commonly include one or more physical, emotional, or behavioral symptoms, that resolve with menses. The range of symptoms is wide, and most commonly are breast tenderness, bloating, headache, mood swings, depression, anxiety, anger, and irritability. To be diagnosed as PMS, rather than a normal discomfort of the menstrual cycle, these symptoms must interfere with daily living, during two menstrual cycles of prospective recording. PMS-related symptoms are often present for about six days. An individual's pattern of symptoms may change over time. PMS does not produce symptoms during pregnancy or following menopause.

Diagnosis requires a consistent pattern of emotional and physical symptoms occurring after ovulation and before menstruation to a degree that interferes with normal life. Emotional symptoms must not be present during the initial part of the menstrual cycle. A daily list of symptoms over a few months may help in diagnosis. Other disorders that cause similar symptoms need to be excluded before a diagnosis is made.

Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, flatulence or upper abdominal pain. People may also experience feeling full earlier than expected when eating. Indigestion is relatively common, affecting 20% of people at some point during their life, and is frequently caused by gastroesophageal reflux disease (GERD) or gastritis.

Indigestion is subcategorized as either "organic" or "functional dyspepsia", but making the diagnosis can prove challenging for physicians. Organic indigestion is the result of an underlying disease, such as gastritis, peptic ulcer disease (an ulcer of the stomach or duodenum), or cancer. Functional indigestion (previously called non-ulcer dyspepsia) is indigestion without evidence of underlying disease. Functional indigestion is estimated to affect about 15% of the general population in western countries and accounts for a majority of dyspepsia cases.