Hard lumps under the skin by the anus and perineum may be caused by perianal abscess, lipoma, folliculitis and so on. 1. Perianal abscess: a purulent infectious disease with recurrent sinusitis that does not heal for a long time. If the infection is caused by poor emptying of the sinuses, it will lead to the appearance of an obvious pus cavity. Early on, there will be localized swelling around the anus and perineal margin subcutaneously, which will lead to localized pain in the anus and the formation of a hard lump in a short period of time. 2. Lipoma: It is a benign soft tissue tumor, usually due to an abnormal genetic mutation leading to the deposition of adipose tissue and the formation of hard lumps. It can be seen under the epithelium of the anus and perineum. In the case of small lipomas, there are usually no obvious symptoms. If the lipoma is more than 5 centimeters, there will be anal swelling, falling sensation, foreign body sensation, constipation and other manifestations. 3. Folliculitis: it is a relatively common skin disease, especially in the buttocks, if we sit for a long time without enough breathability, it is easy to cause mold infections and other infections near the anus, resulting in pore obstruction, the formation of folliculitis and possible hard lumps and so on. Hard lumps under the skin near the anus and perineum may also be caused by other reasons, please go to the hospital in time to clarify the cause of the disease, and follow the doctor’s instructions to carry out reasonable and standardized treatment.