Nausea is a feeling of queasiness or discomfort in the abdomen, which may be accompanied by the urge to vomit. Vomiting is the forceful expulsion of stomach contents through the mouth.

Retching occurs when a person attempts to vomit, but no stomach contents are expelled. It is also called dry heaves. Retching and nausea can occur without vomiting or before vomiting.

Nausea includes uneasiness in the abdomen, but may not lead to vomiting. It may be related to a decrease of the normal motion (motility) in the stomach. Vomiting occurs when a part of the brain receives signals and stimulates action in the stomach and esophagus. Food does not move from the stomach to the intestines as it normally does, but flows back (refluxes) into the stomach. The surrounding muscles contract and the stomach contents are expelled through the mouth. Dry heaves occur when the stomach and its surrounding muscles contract, but the opening at the back of the throat (glottis) remains closed. 

People experience occasional bouts of nausea or vomiting for many reasons. Nausea and vomiting are particularly common in infants and children. In most people, nausea and vomiting are symptoms that pass within a day or two. However, in patients with chronic medical or psychiatric conditions, nausea and vomiting may last for a week or longer.

Nausea and vomiting that occur repeatedly over time can cause a variety of complications, including:

• Dehydration. Prolonged vomiting can lead to loss of fluids in the body, especially when it occurs with diarrhea. Children become dehydrated more quickly than adults and are particularly prone to dehydration from vomiting.
  
  
• Electrolyte imbalance. Electrolytes are substances that are necessary for normal body chemistry and functioning. Severe vomiting can result in loss of electrolytes.
  
  
• Weight loss and/or malnutrition. Severe vomiting can result in weight loss and malnutrition, particularly if it prevents eating.
  
  
• Bruises or tears. Violent retching can occasionally cause bruises or tears in the abdominal wall muscles or in the gastroesophageal junction, where the esophagus and stomach meet. Tears at this junction are called Mallory-Weiss tears.
  
  
• Dental disease. Stomach acid in vomit can damage teeth and gums and lead to dental disease. This complication commonly occurs in eating disorders where patients induce vomiting frequently (e.g., bulimia nervosa).