A two-millimeter foreign body three millimeters below the skin of the wound may be caused by foreign body residue, scar hyperplasia and other reasons. 1. Foreign body residue: due to the injury, foreign body into the wound is not cleaned up, resulting in foreign body residue, such as injury when the impact force is too large and thus lead to wood chips, glass into the wound, generally will appear severe pain. It may also be caused by blood clots formed by postoperative bruising. 2. Scar hyperplasia: due to dermal injury, the wound fibroblast proliferation and collagen overproduction, the wound subcutaneous foreign body sensation. It is recommended to clean the wound in time, sterilize it with iodine and then wrap it with gauze and bandage with pressure. If the wound appears purulent secretion, the surrounding skin appears red, swollen, pain and other symptoms, timely to the hospital, the doctor for treatment.