The redness of the bruised area after hot compress is considered to be due to the following reasons: 1. The bruising is caused by the rupture of the tiny local blood vessels, which increases the permeability of the blood and spills out of the veins and thus causes bruising. The redness of the skin is caused by the allergic reaction of the skin after the application of hot compresses, which is usually accompanied by fever and other symptoms. As there are more reasons for the redness of hot compresses, it needs to be combined with clinical symptoms to determine. If the local pain is reduced after the hot compress, the redness is considered to be caused by the dissipation of blood stasis after the hot compress. If the local pain and itching after hot compress, it is considered to be caused by skin allergy. If the local skin is red and blistered after the hot compress, it is considered to be caused by burns and needs to be stopped in time.