Nausea is the unpleasant subjective sensation that a person feels they are about to vomit, although Nausea can occur without subsequent vomiting. It is a symptom generated through complex interactions among the gastrointestinal tract, brainstem, vestibular system and higher brain centres. People may describe it as queasiness, an unsettled stomach or an urge to be sick. It is not itself a diagnosis and can accompany gastrointestinal infections, medication effects, pregnancy, migraine, motion sickness, metabolic disturbances, anxiety, severe pain and many other conditions. Because its causes are diverse, understanding the associated symptoms and circumstances is often more informative than treating the sensation in isolation.
The physiology of Nausea involves neural pathways that integrate signals from several sources. The gastrointestinal tract can send information through visceral sensory pathways when it detects irritation or abnormal distension. The chemoreceptor trigger zone in the area postrema can detect circulating substances because it lies outside the usual blood-brain barrier protection, while the vestibular apparatus contributes strongly to motion-related nausea. Higher cortical and limbic influences can also generate nausea in response to unpleasant sensory experiences, emotions or learned associations. The vomiting centre in the brainstem coordinates the motor sequence of vomiting when emesis occurs, but nausea and vomiting remain physiologically distinct phenomena.
Common causes of Nausea include gastroenteritis, foodborne illness, medication adverse effects, migraine, pregnancy, motion sickness, alcohol, severe pain and postoperative states. More serious causes can include intestinal obstruction, appendicitis, pancreatitis, myocardial infarction, intracranial pathology, metabolic disturbances and severe infection. The differential diagnosis therefore depends on age, timing, associated symptoms, recent exposures and underlying disease. Nausea after movement suggests vestibular mechanisms, while nausea associated with diarrhoea and abdominal cramps often points towards gastrointestinal disease. Persistent nausea without an obvious explanation warrants consideration of medication, metabolic and structural causes.
Management of Nausea begins with addressing its underlying cause whenever possible. Maintaining hydration is important, particularly if vomiting is also present. Small amounts of fluid taken frequently can be easier to tolerate than large volumes, and avoiding strong smells or foods that provoke symptoms can sometimes help. Antiemetic medicines act through different neurotransmitter pathways, including serotonin, dopamine, histamine, acetylcholine and neurokinin signalling. The appropriate agent depends on the cause, age, pregnancy status, other medicines and potential adverse effects. Treating nausea without recognising an underlying serious condition can be inappropriate when warning symptoms are present.
Nausea can occur with or without Vomiting, and the distinction matters clinically. A person may have persistent nausea while retaining fluids and food, whereas repeated vomiting can rapidly cause dehydration and electrolyte abnormalities. Associated abdominal pain, fever, diarrhoea, headache, neurological symptoms, chest pain or weight loss can provide important clues to the underlying disorder. Nausea accompanied by severe abdominal pain and abdominal distension may suggest obstruction or another acute abdominal process, while nausea with severe headache or neurological deficits can raise concern for neurological disease. Clinical interpretation therefore depends heavily on the broader symptom pattern.
Persistent Nausea can affect nutrition, hydration, sleep, medication adherence and quality of life. Chronic nausea may lead to food avoidance and weight loss, and people can develop anxiety around eating or situations associated with symptom recurrence. In cancer care, Nausea can result from the disease itself, chemotherapy, radiation, opioid analgesics or other medicines, making preventive and anticipatory treatment particularly important. Pregnancy-associated nausea and vomiting likewise range from common symptoms to severe disease causing dehydration and nutritional compromise. The severity of nausea should therefore be judged not solely by subjective discomfort but also by its consequences for intake and functioning.
Diagnosis of Nausea is generally based on history and examination rather than a single diagnostic test. Important questions include when the sensation began, whether it is related to meals or movement, whether vomiting occurs, what the vomit contains, which medicines are being taken and whether there are associated bowel, urinary, neurological or systemic symptoms. Testing may include blood investigations, pregnancy testing, imaging or endoscopy depending on the suspected cause. Red flags such as severe or worsening pain, blood in vomit, severe headache, neurological changes, persistent inability to keep fluids down, chest pain, marked dehydration or suspected poisoning require prompt medical evaluation.
Nausea is sometimes incorrectly treated as synonymous with stomach illness, but its neural mechanisms mean that many non-gastrointestinal conditions can produce it. Motion sickness demonstrates that vestibular signals alone can provoke nausea, while chemotherapy demonstrates that circulating chemical signals can activate nausea pathways. Medication-induced nausea illustrates the importance of pharmacology, and pregnancy demonstrates hormonal and central mechanisms that remain incompletely explained. The term therefore describes a subjective physiological state rather than a particular anatomical disorder. Accurate assessment requires integrating the symptom with timing, triggers, associated manifestations, medication exposure and the wider clinical context.
