Rectal polyp. Light micrograph of a section through a rectal polyp. The rectum is the end portion of the intestines. Polyps are small benign (non-cancerous) growths that arise from the mucous lining of the intestines. The thin outer layer of the polyp, the mucosa, consists of epithelial cells. Beneath the mucosa is the submucosa, which consists of connective tissue. The cause of most polyps is not known, although a diet high in animal fat and red meat and low in fibre may be a risk. Some are caused by diseases, such as familial polyposis or irritable bowel syndrome. Polyps should be surgically removed as they may become malignant (cancerous).