The girl knee area bruise, generally due to the following two reasons: 1, trauma causes: patients inadvertently bumped the knee, resulting in soft tissue damage to the knee, subcutaneous capillary rupture congestion, will form bruises in the knee area. This situation within 48 hours after the injury, you can local cold compress, after 48 hours can take the skin hot compress, generally about a week can disappear; 2, pathological reasons: such as allergic purpura, can cause subcutaneous capillary rupture, the patient will be found in the knee, or other parts of the body bruises. If a girl’s knee area appears bruised for no reason and trauma is ruled out, it is recommended to go to a regular hospital for examination and take appropriate treatment after clarifying the cause.