Hardness below the belly button is caused by intestinal tuberculosis, constipation, intestinal spasm, and intestinal tumors. When Mycobacterium tuberculosis enters the digestive system, it can trigger an attack of intestinal tuberculosis, which is particularly likely to occur at the end of the ileum and in the cecum, which is in the lower right side of the body. Since a swelling is formed during an attack of intestinal tuberculosis, it is important to be alert to an attack of intestinal tuberculosis when a hardness appears on the lower right side of the navel. The lower left part of the navel is the area of the sigmoid colon and rectum, where feces are stored in case of constipation, and can feel hard to the touch because of the dry nature of the feces. In the case of intestinal cramps, the intestine will contract and spasm strongly due to the smooth muscles, so a hard lump will form, and the location of the hard lump is related to the location of the intestinal cramps. However, intestinal cramps are only temporary and disappear after a few minutes. In some people, intestinal tumors are present in the intestine, and in the advanced stage, the tumors will gradually enlarge and even hard lumps can be felt in the abdomen. Patients with intestinal tumors may also have symptoms such as change in bowel habits and mucopurulent stools.