A lump between the caudal vertebrae and the anus may be caused by sebaceous cysts, perianal abscesses, lipomas and other causes. 1. Sebaceous cysts: when the sebaceous glands of the coccyx and anus cause blockage of hair follicles, the hair follicles will not be able to secrete sebum through the mouth of sebaceous glands, thus causing the phenomenon of extrusion, so there will be sebaceous cysts, and sebaceous cysts are mostly presented in the form of lumps. 2. Perianal abscess: most of perianal abscess is caused by bacterial infection in the intestinal tract, and perianal abscess will be formed if you don’t pay attention to the cleanliness of the anus in your daily life, and the main symptom is the appearance of abscess bag around the anus. 3. Lipoma: Lipoma is formed due to the excessive proliferation of normal fat cells, mostly presenting as a mass structure, commonly found in obese patients, the accumulation of fat in the anus will appear between the caudal vertebrae and the anus and there is a lump phenomenon. There is a lump between the caudal vertebrae and the anus, there may be other reasons, it is recommended to go to the hospital for examination, the doctor will be combined with the clinical symptoms to give the appropriate diagnosis, clear causes of timely treatment, to avoid delays in the condition.