what causes a stitch

A stitch, also known as exercise-related transient abdominal pain (ETAP) or side stitch, is a sharp or cramping pain felt in the side of the abdomen, often during physical activity like running. The exact cause of a stitch is not fully understood, but the most supported theory is irritation of the parietal peritoneum—the membrane lining the abdominal cavity and surrounding the organs—which may be aggravated by movement and friction during exercise. Other possible causes include strain on ligaments that attach internal organs (such as the stomach, liver, or spleen) to the diaphragm, shallow or improper breathing, and reduced blood flow or cramping in the diaphragm muscle. Eating or drinking too close to exercise can increase the risk because of additional strain on these ligaments and membranes or blood flow shifts favoring digestion. Stitches can occur in various activities involving torso movement, such as running, swimming, and cycling, and they can cause pain sometimes felt in the abdomen, sides, or even shoulder tip due to nerve involvement.