A 2cmx1.5cmx0.4cm swelling in the left posterior lumbar region may be subcutaneous lipoma, folliculitis, sebaceous cyst and other diseases. Generally, medication and surgical treatment are prescribed by doctors. 1. Subcutaneous lipoma: it is a benign tumor that occurs in the cells of subcutaneous tissues, the cause of which is still unclear and may be related to genetic factors. For relatively small subcutaneous lipoma, no special treatment can be done, and larger tumors can be done lipomectomy. 2. Folliculitis: Folliculitis is mainly due to the skin inflammation caused by Staphylococcus aureus, due to the immune response can trigger swelling of purulent papules, which can lead to the left side of the lower back part of the length of 2cmx1.5cmx0.4cm swelling. Usually follow the doctor’s prescription of topical antibiotics such as mupirocin ointment can be relieved, the pain in the swollen area can also be surgically incised and drained to relieve the symptoms. 3. Sebaceous cysts: they are benign tumors that occur in the skin and are usually found in the head, back and waist. Inflammation should be controlled as soon as possible after diagnosis, and then removal surgery should be done. If there is a swelling on the right side of the lower back, do not do any treatment on your own before the specific nature of the swelling is clarified, but consult the doctor in time to get a clear diagnosis and follow the doctor’s instructions.