Irritable bowel syndrome (IBS) is a common disorder that affects the large intestine. Signs and symptoms include cramping, abdominal pain, bloating, gas, and diarrhea or constipation, or both. IBS is a chronic condition that you'll need to manage long term.

Only a small number of people with IBS have severe signs and symptoms. Some people can control their symptoms by managing diet, lifestyle and stress. More-severe symptoms can be treated with medication and counseling.

Symptoms

The signs and symptoms of IBS vary but are usually present for a long time. The most common include:

• Abdominal pain, cramping or bloating that is related to passing a bowel movement
• Changes in appearance of bowel movement
• Changes in how often you are having a bowel movement

Other symptoms that are often related include bloating, increased gas or mucus in the stool.

See your doctor if you have a persistent change in bowel habits or other signs or symptoms of IBS. They may indicate a more serious condition, such as colon cancer. More-serious signs and symptoms include:

Weight loss

Diarrhea at night

Rectal bleeding

Iron deficiency anemia

Unexplained vomiting

Difficulty swallowing 

Causes

The precise cause of IBS isn't known. Factors that appear to play a role include:

Muscle contractions in the intestine. The walls of the intestines are lined with layers of muscle that contract as they move food through your digestive tract. Contractions that are stronger and last longer than normal can cause gas, bloating and diarrhea. Weak intestinal contractions can slow food passage and lead to hard, dry stools.

Nervous system. Abnormalities in the nerves in your digestive system may cause you to experience greater than normal discomfort when your abdomen stretches from gas or stool. Poorly coordinated signals between the brain and the intestines can cause your body to overreact to changes that normally occur in the digestive process, resulting in pain, diarrhea or constipation.

Severe infection. IBS can develop after a severe bout of diarrhea (gastroenteritis) caused by bacteria or a virus. IBS might also be associated with a surplus of bacteria in the intestines (bacterial overgrowth).

Early life stress. People exposed to stressful events, especially in childhood, tend to have more symptoms of IBS.

Changes in gut microbes. Examples include changes in bacteria, fungi and viruses, which normally reside in the intestines and play a key role in health. Research indicates that the microbes in people with IBS might differ from those in healthy people.