Your skin starts going through some changes after 24 hours Nature is very efficient at breaking down human corpses. When you die your heart stops pumping blood around your body, thus depriving your cells of oxygen, which rapidly begin to die. Decomposing starts almost immediately, with the skin going through several changes in colour as the blood stops circulating leaving the body an ashen color. However different cells die at different rates. For example, brain cells die within a few minutes, whilst skin cells can survive over 24 hours after death. Soon after death rigor mortis occurs, which is caused by a complex chemical reaction (involving lactic acid and myosin), which forms a gel like substance which creates the body's stiffness. Rigor mortis lasts approximately 24 hours (depending upon ambient temperature).