Human decomposition is a natural process involving the breakdown of tissues after death. While the rate of human decomposition varies due to several factors, including weather, temperature, moisture, pH and oxygen levels, cause of death, and body position, all human bodies follow the same four stages of human decomposition.
The four stages of human decomposition
According to Dr. Arpad A. Vass, a Senior Staff Scientist at Oak Ridge National Laboratory and Adjunct Associate Professor at the University of Tennessee in Forensic Anthropology, human decomposition begins around four minutes after a person dies and follows four stages: autolysis, bloat, active decay, and skeletonization.
Stage One: Autolysis
The first stage of human decomposition is called autolysis, or self-digestion, and begins immediately after death. As soon as blood circulation and respiration stop, the body has no way of getting oxygen or removing wastes. Excess carbon dioxide causes an acidic environment, causing membranes in cells to rupture. The membranes release enzymes that begin eating the cells from the inside out.
Rigor mortis causes muscle stiffening. Small blisters filled with nutrient-rich fluid begin appearing on internal organs and the skin’s surface. The body will appear to have a sheen due to ruptured blisters, and the skin’s top layer will begin to loosen.
Stage Two: Bloat
Leaked enzymes from the first stage begin producing many gases. The sulfur-containing compounds that the bacteria release also cause skin discoloration. Due to the gases, the human body can double in size. In addition, insect activity can be present.
The microorganisms and bacteria produce extremely unpleasant odors called putrefaction. These odors often alert others that a person has died, and can linger long after a body has been removed.
Fluids released through orifices indicate the beginning of active decay. Organs, muscles, and skin become liquefied. When all of the body’s soft tissue decomposes, hair, bones, cartilage, and other byproducts of decay remain. The cadaver loses the most mass during this stage.
Stage Four: Skeletonization
Skeletonization refers to the final stage of decomposition, during which the last vestiges of the soft tissues of a corpse or carcass have decayed or dried to the point that the skeleton is exposed. By the end of the skeletonization process, all soft tissue will have been eliminated, leaving only disarticulated bones.
In a temperate climate, it usually requires three weeks to several years for a body to completely decompose into a skeleton, depending on factors such as temperature, humidity, presence of insects, and submergence in a substrate such as water. In tropical climates, skeletonization can occur in weeks, while in tundra areas, skeletonization may take years or may never occur, if subzero temperatures persist. Natural embalming processes in peat bogs or salt deserts can delay the process indefinitely, sometimes resulting in natural mummification.
Body Decomposition Timeline
24-72 hours after death— the internal organs decompose.
3-5 days after death— the body starts to bloat and blood-containing foam leaks from the mouth and nose.
8-10 days after death — the body turns from green to red as the blood decomposes and the organs in the abdomen accumulate gas.
Several weeks after death — nails and teeth fall out.