ReviewWhat is nausea? A historical analysis of changing views

- Nausea was historically equated with seasickness.
- The prodromal signs and symptoms preceding vomiting can vary depending on the emetic trigger.
- Triggering stimuli used in laboratory studies of nausea may not elicit the same prodromal indicators as “real world” stimuli.
- A definition of nausea must consider that prodromal signs and symptoms can vary between individuals and triggering mechanisms.
- A variety of neural pathways can be activated by emetic stimuli, depending on the responses evoked in an individual.

The connotation of “nausea” has changed across several millennia. The medical term 'nausea' is derived from the classical Greek terms ναυτια and ναυσια, which designated the signs and symptoms of seasickness. In classical texts, nausea referred to a wide range of perceptions and actions, including lethargy and disengagement, headache (migraine), and anorexia, with an awareness that vomiting was imminent only when the condition was severe. However, some recent articles have limited the definition to the sensations that immediately precede emesis. Defining nausea is complicated by the fact that it has many triggers, and can build-up slowly or rapidly, such that the prodromal signs and symptoms can vary. In particular, disengagement responses referred to as the “sopite syndrome” are typically present only when emetic stimuli are moderately provocative, and do not quickly culminate in vomiting or withdrawing from the triggering event. This review considers how the definition of “nausea” has evolved over time, and summarizes the physiological changes that occur prior to vomiting that may be indicative of nausea. Also described are differences in the perception of nausea, as well as the accompanying physiological responses, that occur with varying stimuli. This information is synthesized to provide an operational definition of nausea.