(from Greek nausia, “seasickness”), feeling of discomfort in the pit of the stomach that is associated with a revulsion for food and an expectation that vomiting will follow, as it often does. Nausea results from the irritation of nerve endings in the stomach or duodenum, which in turn stimulate centres in the brain that control nausea and vomiting. Nausea can be a symptom of disorders ranging from the trivial to the serious. It is most commonly caused by indigestion, by motion sickness, or by pregnancy. Nausea can result from eating too rapidly or from experiencing emotional stress during or just after a meal. The nausea experienced in seasickness and airsickness is caused by a disturbance of the semicircular canals of the inner ear, which are the organs of balance. The nausea sometimes experienced in the early months of pregnancy is called morning sickness and usually occurs at breakfast time. It recurs daily for two or three weeks and then disappears without any treatment. Nausea may also arise from any of the causes of an abnormal lack of appetite—for example, shock, pain, intracranial pressure, badly fitting dentures, or disease of the liver or of the kidneys. Simple nausea is relieved by vomiting.