Numbness of ring finger and little finger after pressing a lump growing under the skin of the arm is a case of subcutaneous cyst or lipoma compressing the nerves (e.g. ulnar nerve), which needs timely medical treatment. Numbness of ring finger and little finger after pressing a lump growing under the skin of the arm is mainly considered as subcutaneous cyst or lipoma, especially growing near the nerves, and the numbness of the fingers occurs after pressing due to the compression of the local nerves, resulting in abnormal nerve conduction function. However, the nature of the specific swelling, but also need to consult a doctor in a timely manner, local ultrasound or biopsy, in order to finalize the diagnosis of the case shall prevail. When compression of nerves occurs, timely excision is also needed to avoid long-term compression due to the continuous growth of the swelling. The specific need for timely medical treatment, subject to the recommendations of the doctor.