Diarrhea is an increase in the liquidity and/or volume of stool or the frequency of bowel movements. It may be mild, moderate or severe and can have an impact on normal activities. Diarrhea is extremely common in children, particularly before the age of 3 or 4.

The average frequency of bowel movements and firmness of stool can vary greatly from child to child. Thus, it is important to note any significant changes in what is normal for a particular child. Children with diarrhea have stool that ranges from soft to liquid in texture and brown to clear in color. During bouts of diarrhea, they typically have bowel movements more than three times a day.

Diarrhea is caused by a disruption of the normal process of digestion. Normal digestion involves food traveling from the stomach to the small intestine, where most nutrients are absorbed. By the time it gets to the colon, only waste material remains. The colon absorbs most of the water from the waste and passes the stool along via muscle contractions (peristalsis) to the rectum at the end of the digestive tract. Diarrhea occurs when too much fluid remains in the intestines as stool travels through the digestive tract. When this occurs, the stool that eventually is passed is loose and watery.

Younger children with diarrhea tend to have stools that are more watery than older children. The color of diarrhea also varies from child to child and may include light brown, yellow or green stools.

Too much fluid in the intestines can be caused by several different types of digestive dysfunction, including:

• The small intestine and colon may fail to absorb enough nutrients and fluids from stool, making the stool loose and watery.
  
  
• The intestines may be stimulated to secrete water, salt or other fluids into the digestive tract, making stool runny. This stimulation can occur as the result of infection, disease or the presence of certain other substances (e.g., castor oil, excess bile acids).
  
  
• Food may pass through the intestines too quickly or in too large an amount to be properly absorbed. The rapid transit of stool through the digestive tract is a common cause of diarrhea.

Most cases of diarrhea in children are the result of an infection with a gastrointestinal virus. Children often are infected with these viruses when they are exposed to the virus in childcare centers, playgrounds, school classrooms or children’s hospitals.

Acute diarrhea (lasting less than four weeks) is the most common type of diarrhea. Most cases of acute diarrhea are caused by infection or antibiotic treatment, and resolve spontaneously. However, frequent, explosive episodes of diarrhea can lead to dehydration, particularly in small children. This is a potentially dangerous situation that demands prompt medical attention.