Hard lumps below the belly button may be caused by sebaceous cysts, fibroids, hernias, intestinal tumors and other causes. 1. Sebaceous cysts: If the sebaceous glands in the skin below the navel are blocked, sebaceous secretions may accumulate and form hard lumps. 2. Fibroid tumors: they are found in the limbs and abdomen and can manifest as painless hard lumps. 3. Hernia: it is often found unintentionally that the lump in the abdomen protrudes from the body surface, which can be manifested as a hard lump below the navel. 4. Intestinal tumors: If there is a tumor in the intestinal part below the belly button, it can manifest as a hard lump as the tumor grows. Hard lumps below the navel may also be caused by other reasons, it is recommended to go to the hospital in time, to clarify the cause of the disease, under the guidance of the doctor for standardized treatment.