The hard lump inside the wound may be caused by foreign body residue, thread knot, hyperplastic scar and other factors. 1. Foreign body residue: the wound is caused by trauma, and there is foreign body residue inside the wound, which will cause hard lumps inside the wound, and there will be continuous pain, oozing and other symptoms. 2. Thread knot: the wound is relatively large, may need to be treated with suture, after the subcutaneous suture, there may be thread knots, which will be manifested as localized hard lumps. 3. Proliferative scarring: When the wound site is infected, proliferative scarring may occur, which will be felt as a hard lump inside the wound, and may be accompanied by pain and itching and other abnormal manifestations. If there is a hard lump inside the wound and other abnormal manifestations, it is recommended to consult a doctor for examination to clarify the specific cause and timely treatment.