Many pre-existing conditions determine the rate of tissue breakdown following a death. The first may be overall weight or body mass which is a pre-disposing condition of certain specific diseases. Death occurs in stages. Tissue breakdown may take from several days up to years. At all stages of decomposition, insect infiltration occurs on and in the body. The initial or fresh stage of decomposition occurs during the first few days with no physical signs.

  Homeostasis of the body has ceased allowing cellular and soft tissue changes to occur because of the process of autolysis. This is the destruction of the cells and organs due to an aseptic chemical process. At this point, the body enters algor mortis – the cooling of the body to that of its surroundings. When the body’s cells reach the final stage of autolysis, an anaerobic environment is created that is an environment wherein oxygen is not present.

  This allows the body’s normal bacteria to breakdown the remaining carbohydrates, proteins and lipids. The products from the breakdown create acids, gases and other products which cause volatile organ compounds (VOC) and putrefactive effects.

  Substances produced during the fresh stage of decomposition attract a variety of insects. Dipteral insects begin to lay their eggs in the body during this stage, especially members of the calliphoridae family. If the body is on the ground or buried in soil, there is also considerable insect activity by insects that live in the soil surrounding the body. The reasoning for this is simple. A dead human body serves as an excellent source of decaying matter on which to feed.

  Odor, color changes and bloating of the body during early stages of protein breakdown must be neutralized during putrefaction in the lower part of the abdomen. Body tissue will begin to turn green due to bacterial activity in the cecum. Bacterial breakdown of hemoglobin into sulfhemoglobin also causes a green color change. A formation of gases enters the abdomen which forces liquids and feces out of the body orifices. The gases also enter the neck and face causing swelling of the mouth, lips and tongue.

  Due to this swelling and misconfiguration of the face, identification of the body can be difficult. Bacteria also enter the venous system causing blood to hemolyze. This leads to the formation of red streaks along the veins. This color soon changes to green, through a process known as marbleization. It can be seen on the shoulders, chest and shoulder area and thighs. The skin can develop blisters containing serous fluid. The skin also becomes fragile leading to skin slip.