Nausea and vomiting are symptoms of an underlying disease and not a specific illness. Nausea is the sensation that the stomach wants to empty itself, while vomiting or throwing up, is the act of forcible emptying of the stomach.

Vomiting is a violent act in which the stomach has to overcome the pressures that are normally in place to keep food and secretions within the stomach.

The stomach almost turns itself inside out - forcing itself into the lower portion of the esophagus (the tube that connects the mouth to the stomach) during a vomiting episode.

There are numerous causes of nausea and vomiting. These symptoms may be due; acute gastritis, central causes (signals from the brain), association with other illnesses remote from the stomach, medications and medical treatments and mechanical obstruction of the bowel.

There are also central causes that are signals from the brain that cause nausea and vomiting. Headache especially migraine is commonly associated with nausea and vomiting.

It may be due to inner ear complaints such as Motion sickness, labyrinthitis, and benign postural vertigo. Head injury; any illness or injury that increases the pressure inside the skull can cause vomiting.

This rise in intracranial pressure may be due to brain swelling from trauma for example, concussion or head trauma, infection such as meningitis or encephalitis, tumor, abnormal electrolyte and water balance in the bloodstream.

Noxious stimulus, for example certain smells or sounds can cause centrally mediated nausea and vomiting. Whether it is the pain of a broken bone or the emotional shock of observing an event, vasovagal events can cause significant symptoms.

In a vasovagal episode, the vagus nerve (one of the nerves that helps control basic body functions like heart rate, breathing, and blood pressure) is overly stimulated and cause the heart rate to slow and blood vessels to dilate. This decreases the blood flow to the brain and causes fainting known as a syncopal episode.

Some common nausea and vomiting complaints are associated with illness. Persons with diabetes may develop nausea because of gastro paresis, a condition in which the stomach fails to empty properly and is likely due to the generalized neuropathy (failure of the nerves in the body to send proper signals to and from the brain) that is a complication of the disease.

People with diabetes can also develop nausea and vomiting should their blood sugars become abnormally high or low (hyperglycemia, hypoglycemia) because the sugar and insulin balance is disturbed.

Many illnesses associated with the intra-abdominal organs have symptoms of nausea and vomiting.

These include digestive organ diseases for example hepatitis, gallbladder disease, pancreatitis,  inflammatory bowel disease,  kidney diseases (for example, kidney stones, infection, kidney failure), some forms of cancer.

Vomiting as an atypical symptom of another disease; some illnesses will cause nausea and vomiting, even though there is no direct involvement of the stomach or gastrointestinal tract.

Heart attack victims may experience nausea and vomiting as an atypical presentation of angina, especially if the myocardial infarction affects the inferior or lower part of the heart.

Lung infections for example, pneumonia and bronchitis may also cause nausea and vomiting, especially if the area of lung involved is near the diaphragm, the muscle that separates the chest from the abdomen.

Sepsis; an overwhelming body infection spread through the bloodstream may also be associated with nausea and vomiting.

Eating disorders; Patients with bulimia will have self-induced vomiting, purging as part of their psychiatric illness

Side effects from medications; the side effect of many medications include stomach irritation, nausea and vomiting. Anti-cancer drugs are notorious irritants for example, chemotherapy treatment.

Narcotic pain medications, anti-inflammatory medications including both steroids like prednisone and non-steroidal medications like ibuprofen and antibiotics all have nausea and vomiting listed as common side effects.

Radiation therapy: Nausea and vomiting is associated with radiation therapy. Abdominal pain and distention, nausea and vomiting, and inability to pass flatus (gas) or have a bowel movement are hallmarks of bowel obstruction.

Due to a variety of potential reasons, the small intestine becomes blocked and does not allow contents to pass through to the colon. This acts like a dam in which food, fluid, and secretions back up causing the symptoms of an obstruction.

Vomiting in pregnancy is especially common in the first trimester and is due to hormone level changes in the bloodstream.

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