Hard lumps between the scrotum and anus may be boils, sebaceous cysts, hematomas, perianal abscesses, etc., which require further differential diagnosis by a doctor. 1. Boils: If a single hair follicle between the scrotum and anus is infected by pathogenic bacteria such as staphylococcus, it can cause a localized boil, which is manifested by the occurrence of a hard lump. 2. Sebaceous cysts: If the sebaceous secretions located between the scrotum and the anus cannot be discharged normally, it can cause the appearance of hard lumps. 3. Hematoma: If the patient suffers trauma to the perineum, it may lead to local tissue injury and the appearance of hematoma. 4. Perianal abscess: If bacterial infection occurs in the anorectal tissues and interstitial space, the local area will cause suppurative infection, which can form a hard lump under the skin between the anus and scrotum, which is hard to touch and gradually increases in size, and can be accompanied by redness, swelling, hot pain or fluctuating sensation, and other phenomena. It is recommended that people with hard lumps between the scrotum and anus go to the hospital in time, to clarify the cause of the disease, and standardize the treatment under the guidance of the doctor, so as not to delay the condition.