Nausea is the sensation of having an urge to vomit. Vomiting is forcing the contents of the stomach up through the esophagus and out of the mouth.

Your body has a few main ways to respond to an ever-changing, wide variety of invaders and irritants. Sneezing ejects the intruders from the nose, coughing from the lungs and throat, diarrhea from the intestines, and vomiting from the stomach.

Vomiting is a forceful action accomplished by a fierce, downward contraction of the diaphragm. At the same time, the abdominal muscles tighten against a relaxed stomach with an open sphincter. The contents of the stomach are propelled up and out.

You may have more saliva just before vomiting.

Vomiting is a complex, coordinated reflex orchestrated by the vomiting center of the brain. It responds to signals coming from:

• The mouth, stomach, and intestines
• The bloodstream, which may contain medicines or infections
• The balancing systems in the ear (motion sickness)
• The brain itself, including unsettling sights, smells, or thoughts

An amazing variety of stimuli can trigger vomiting, from migraines to kidney stones. Sometimes, just seeing someone else vomit will start you vomiting, in your body's effort to protect you from possible exposure to the same danger.

Vomiting is common. Almost all children will vomit several times during their childhood. In most cases, it is due to a viral gastrointestinal infection.

“Spitting up,” the gentle sloshing of stomach contents up and out of the mouth, sometimes with a burp, is an entirely different process. Some spitting up is normal for babies, and usually gets gradually better over time. If spitting up worsens or is more frequent, it might be reflux disease. Discuss this with your child's doctor.

Most of the time, nausea and vomiting do not require urgent medical attention. However, if the symptoms continue for days, they are severe, or you cannot keep down any food or fluids, you may have a more serious condition.

Dehydration is the main concern with most vomiting. How fast you become dehydrated depends on your size, frequency of vomiting, and whether you also have diarrhea.

The following are possible causes of vomiting:

• Viral infections
• Medications
• Seasickness or motion sickness
• Migraine headaches
• Morning sickness during pregnancy
• Food poisoning
• Food allergies
• Brain tumors
• Chemotherapy in cancer patients
• Bulimia
• Alcoholism

• Congenital pyloric stenosis, a constriction in the outlet from the stomach (the infant vomits forcefully after each feeding but otherwise appears to be healthy)
• Food allergies or milk intolerance
• Gastroenteritis (infection of the digestive tract that usually causes vomiting with diarrhea)
• Gastroesophageal reflux
• An inborn error of metabolism
• Hole in the bottle nipple may be wrong size, leading to overfeeding
• Infection, often accompanied by fever or runny nose
• Intestinal obstruction, evidenced by recurring attacks of vomiting and crying or screaming as if in great pain
• Accidentally ingesting a drug or poison

Call the doctor immediately or take the child to an emergency care facility if you suspect poisoning or drug ingestion!

It is important to stay hydrated. Try steady, small amounts of clear liquids, such as electrolyte solutions. Other clear liquids -- such as water, ginger ale, or fruit juices -- also work unless the vomiting is severe or it is a baby who is vomiting.

For breastfed babies, breastmilk is usually best. Formula-fed babies usually need clear liquids.

Don’t drink too much at one time. Stretching the stomach can make nausea and vomiting worse. Avoid solid foods until there has been no vomiting for six hours, and then work slowly back to a normal diet.

An over-the-counter bismuth stomach remedy like Pepto-Bismol is effective for upset stomach, nausea, indigestion, and diarrhea. Because it contains aspirin-like salicylates, it should NOT be used in children or teenagers who might have (or recently had) chickenpox or the flu.

Most vomiting comes from mild viral illnesses. Nevertheless, if you suspect the vomiting is from something serious, the person may need to be seen immediately.

If you have morning sickness, ask your doctor about the many possible treatments.

The following may help treat motion sickness:

• Lying down
• Over-the-counter antihistamines (such as Dramamine)
• Scopolamine prescription skin patches (such as Transderm Scop) are useful for extended trips, such as an ocean voyage. Place the patch 4 - 12 hours before setting sail. Scopolamine is effective but may produce dry mouth, blurred vision, and some drowsiness. Scopolamine is for adults only. It should NOT be given to children.

Call 911 or go to an emergency room if you think vomiting is from poisoning or a child has taken aspirin.

Call if the person has:

• Vomiting longer than 24 hours
• Blood or bile in the vomit
• Severe abdominal pain
• Headache and stiff neck
• Signs of dehydration

Signs of dehydration include:

• Increased thirst
• Infrequent urination or dark yellow urine
• Dry mouth
• Eyes that appear sunken
• Crying without tears
• Loss of normal skin elasticity (if you touch or squeeze the skin, it doesn't bounce back the way it usually does)

You should also call if:

• A young child is lethargic or has marked irritability.
• An infant vomits repeatedly.
• A child is unable to retain any fluids for 8 hours or more.
• Vomiting is recurrent.
• An adult is unable to retain any fluids for 12 hours or more.
• There is a decrease in urination (including a baby who is not wetting the normal amount of diapers).
• Nausea persists for a prolonged period of time (in a person who is not pregnant).

Your health care provider will perform a physical examination, particularly to look for signs of dehydration.

To help diagnose the cause of the nausea or vomiting, your doctor will ask medical history questions, such as:

• Are you vomiting fresh blood? Do you have repeated episodes of vomiting blood?
• Are you vomiting material that looks like coffee grounds?
• Are you vomiting undigested food?
• Are you vomiting greenish material?
• Is the nausea or vomiting severe enough to cause unintentional weight loss?
• Is the vomiting self-induced?
• Have you been traveling? Where?
• What medications do you take?
• Did other people that ate at the same location as you have the same symptoms?
• Are you pregnant or could you be pregnant?
• When did the vomiting begin? How long has it lasted?
• Does it occur several hours after meals?
• What other symptoms are also present -- abdominal pain, fever, diarrhea, poor skin turgor, other signs of dehydration, abdominal swelling, headaches?

The following diagnostic tests may be performed:

• Blood tests (such as CBC with differential and basic electrolytes)
• Urinalysis
• X-rays of the abdomen

If dehydration is severe, you may need intravenous fluids. This may require hospitalization, although it can often be done in the doctor's office. The use of antivomiting drugs (anti-emetics) is controversial, and they should be used only in severe cases.

A number of medicines are effective at preventing vomiting. In some situations, preventing the vomiting makes life much better.

Koch KL. Nausea and vomiting during pregnancy. Gastroenterol Clin North Am. 2003; 32(1): 201-234, vi.

Quigley EM. AGA technical review on nausea and vomiting. Gastroenterology. 2001; 120(1): 263-286.

This article uses information by permission from Alan Greene, M.D., © Greene Ink, Inc.