Blood contains protein, inorganic salts, red blood cells and platelets. Inorganic salts are mainly iron ions. Bivalent iron ion (light green) will be oxidized to trivalent iron ion (reddish brown) when it meets air, and some compounds will be formed by combining with protein, which is difficult to wash off. Protein will be denatured by heat and stick to clothes, so when fresh blood sticks to clothes, don't wash it with hot water, just put it in cold water and put some soap or sulfur soap on it for a while. For old blood stains, you can also wash them repeatedly with sulfur soap. If it is white clothes, you can directly use 84 disinfectant, and its bleachability can remove all the colors on the clothes.