Bruising of the hand after a collision is caused by subcutaneous hemorrhage or capillary bleeding, as well as leakage of surrounding tissue fluid. Initially, the bruising appears as subcutaneous bruising with lump formation and pain. Ice or cold towels should be applied outside to cool the hand and stop the bleeding, and to prevent further expansion of the lump when compressing it. If the bruise still exists after one or two days, hot towels, hot baths or hot baths are needed to accelerate blood circulation in the hand and eliminate the bruise more quickly.