The precise causes of IBS are unknown. The gut and all that it entails is a complex system within the human body. Your gut is responsible for a large portion of your immune system and the production of serotonin. Additionally, the microbiome found in the intestine is a balance of bacteria that can influence the health of the entire body. Doctors believe that the muscles and nerves within the bowels of an IBS patient are overly sensitive. They will contract and relax at an abnormal rate which results in cramping and pain. When the muscles force food to pass through the intestines too quickly it results in gas, bloating, diarrhea, or constipation. It is thought that the contractions could be in reaction to certain foods, environmental factors or other stimulants.