Diarrhea can be either short-term (acute) or long-term (chronic). Virtually all children experience the severe and sudden development of acute diarrhea at some point. It is usually short-lived (a few days) and runs its course without need for medication. Acute diarrhea is most often caused by infection (infectious diarrhea), but may also be a side effect of many different prescription or over-the-counter medications.

Chronic diarrhea, on the other hand, lasts for four weeks or more and may indicate a more serious problem requiring treatment. Irritable bowel syndrome (IBS) can cause chronic diarrhea and can affect children. Malabsorption of certain foods is a common cause of chronic diarrhea in children.  

Diarrhea can be categorized into different types, depending on the processes that drive them. Food that passes too quickly through the intestines or in too large an amount to be properly absorbed is a common cause of diarrhea. Additional types of diarrhea by process include:

• Osmotic diarrhea. Occurs when sugars (e.g., lactose, fructose), sugar alcohols (e.g., sorbitol) and some minerals (e.g., magnesium, sulfate, phosphate) in the intestines fail to be absorbed into the body. These unabsorbed substances draw water into the intestines, causing watery stool. Diarrhea caused by lactose intolerance is an example of osmotic diarrhea. Sorbitol is also a common cause of this type of diarrhea. Typically, osmotic diarrhea goes away when foods containing these elements are removed from a patient’s diet.
  
  
• Secretory diarrhea. Occurs when the intestines release water and salt into the stool, making it runny. This can be due to numerous causes, the most common being infections that release toxins. The toxic substances interfere with the intestines, causing them to secrete water and salt. Secretory diarrhea can be due to poor absorption of bile acids and fatty acids by the intestines. This may occur in people with certain medical conditions, such as celiac sprue and inflammatory bowel disease (IBD). Cancerous tumors can also stimulate secretions that lead to secretory diarrhea.
  
  Children with digestive systems that move digestive products too quickly are also prone to secretory diarrhea, because the intestines do not have enough time to absorb fluid.
  
  
• Exudative diarrhea. Occurs when inflammation or irritation of the lining of the colon causes the release of blood, mucus or other fluids. This type of diarrhea can be caused by a number of conditions (e.g., IBD, tuberculosis, some cancers).  

It is important to note that different types of diarrhea may occur at the same time. For example, it is rare that children who see a physician about their diarrhea have solely osmotic or solely secretory diarrhea. Some viral or inflammatory conditions can cause both to occur simultaneously.