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 muscle. At the same time, the abdominal muscles tighten against a relaxed stomach with an open gastroesophageal sphincter. The contents of the stomach are propelled up and out.

As part of a bodily reflex, you may produce 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
• Peptic ulcer in the stomach outlet (pylorus)

These are possible causes of vomiting in infants (0 - 6 months):

• 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!