A small lump under a man’s breast is mainly considered to be related to breast diseases, subcutaneous space-occupying lesions and other diseases. 1. Breast diseases: such as breast nodules, abnormal development of the breast, etc., can lead to the appearance of small bumps under the breast. 2. Subcutaneous space-occupying lesions: sebaceous cysts, lipomas, fibrous tumors, etc. under the breast cause local swelling, which is manifested by the appearance of small bumps under the breast. 3. Other diseases: such as malignant tumor of lung, lymph node cancer under breast, bone tumor and bony bumps on ribs can also lead to this symptom. The appearance of this disease may also be related to other causes. It is suggested that patients should go to regular hospitals as soon as possible to clarify the cause of the disease, and combined with the examination results, actively treat under the guidance of doctors.