The cause of irritable bowel syndrome (IBS) is unknown, and there is no apparent disease of the bowel involved. Rather, IBS is related to highly stimulated or reactive nerves and muscles in the large intestine. Research has shown that children with IBS are more sensitive to pain, discomfort and fullness than children without the condition.

In addition, children with IBS are especially sensitive to stress and conflicts, and such emotional trauma is strongly associated with episodes of IBS. Many nerves inside the intestines connect them to the brain. These nerves control functioning and can react adversely to stress. Intestinal muscles may contract too much or too little, leading to chronic diarrhea, constipation or both symptoms. Teething, illness, moving to a new town, starting a new school, family turmoil and other trauma are all potential stress triggers of IBS in children.

Certain foods are also known to trigger IBS symptoms in many children. They include:

• Caffeine (e.g., sodas)
• Chocolate
• Fast foods
• Greasy foods
• Spicy foods
• Carbonated beverages
• Milk and other dairy products (especially in lactose-intolerant children)

Eating large meals may cause too much food to be passed through the digestive tract at once and can lead to nutrient and fluid absorption problems, triggering IBS symptoms.

Other sources of IBS symptoms include:

• Gas. When the intestines are distended due to trapped gas, this can cause abdominal pain and cramping in children with IBS. Activities such as chewing gum or eating meals quickly can lead to the inadvertent swallowing of air and cause gas.
  
  
• Medications. Some medications can negatively affect the digestive system (e.g., cause diarrhea or constipation) and may aggravate symptoms in children with IBS.
  
  
• Menstruation. Girls with IBS may experience more severe symptoms during their menstrual periods.
  
  
• Traumatic life events. Some studies have shown that IBS is more common in people with a history of physical, verbal or sexual abuse.

Research also suggests that children with low birth weight appear to be more likely to develop IBS than those who weigh more than 5.5 pounds at birth.

Among children, boys and girls are equally likely to be diagnosed with IBS. In contrast, adult women are much more likely than adult men to be diagnosed with IBS in Western nations.