Rectal polyp. Coloured scanning electron micrograph (SEM) of the surface of 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 surface of the polyp, the mucosa, consists of epithelial cells. 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 factor. Some polyps are caused by diseases, such as familial polyposis or irritable bowel syndrome. Polyps should be surgically removed as they may become malignant (cancerous). Magnification: x1500 when printed 10 centimetres wide.