Human Body Decomposition: Stages, Factors, and Forensic Significance

Introduction to Taphonomy and Early Post-Mortem Changes

The branch of science that investigates the decomposition of the human body is known as taphonomy, which encompasses the study of phenomena such as biostratinomy, decomposition, diagenesis, and epibiont encrustation. Decomposition may be defined as the process whereby the body is reduced into simpler forms of matter. The process of decomposition is affected in varying degrees by a number of factors. These include the following aspects, listed in the order of their commonly assumed importance with regard to the rate of decomposition:

The first activity of bodily decomposition is the growth of various bacteria within the body at the moment of death. This occurs because the body's natural defense mechanisms against bacteria are no longer functional. The bacteria then begin to dissolve the body from within, producing gas. Other features at the time of death include tautness of the skin and the loss of sphincter tone (McLemore, J. 1993).

Additional early characteristics include pallor of the skin, lips, and fingernails, as well as flatness of the eyes due to fluid loss. The appearance of the blood also changes notably: "The blood, which has become dark purple because of the loss of oxygen, sinks due to the force of gravity and settles on the underside of the body about 30 minutes after death" (Health). Various cells in the body die at different rates — brain cells typically die within four to seven minutes, while skin cells may still be alive after 24 hours.

Livor mortis takes place within a few hours of death. In this process, "blood pools at the lowest portion of the anatomy; often referred to as lividity," and is characterized by large dark-red splotches on the corpse, while the rest of the body appears much paler than normal (Chemistry).

Rigor mortis sets in within four hours of death. It is caused by the lack of adenosine triphosphate (ATP), which provides the energy required for muscle contraction and relaxation (McLemore, J. 1993). Rigor mortis is essentially the state the dead body achieves when the oxygen supply to the muscles ceases. The cells within the body continue anaerobic respiration, producing lactic acid that causes muscular stiffening. After approximately 36 hours — depending on temperature and various other variables — rigor mortis ceases, at which point cellular enzymes are released and precipitate further decomposition.

The stiffening associated with rigor mortis occurs first in the smaller muscles and then advances throughout the body. There are numerous forensically important factors here. For example, "the process of rigor mortis can be accelerated if there was violent exertion before death because the supply of ATP has been used up. Rigor mortis can also be delayed in cases of slow death, such as death by carbon monoxide poisoning where there was no struggle" (McLemore, J. 1993).

Another early sign of decomposition relevant to forensic investigation is the production of ammonia (NH₃) in the lungs relatively soon after death. Because ammonia is lighter than air and diffuses rapidly, the rate of its production decreases with time after death, providing a potential forensic marker.

Decomposition in fact begins during the process of rigor mortis. Although the body is acidic due to the presence of lactic acid during this period, insect larvae can "still feed on serum between the muscle fibers and because the larvae excrete ammonia, they eventually neutralize the acid" (Decomposition).

In terms of the overall timeline, after three days the gas inside the corpse forms blisters on the skin, and the body becomes swollen with fluids leaking from the orifices (McLemore, J. 1993). After approximately three weeks, "the skin, hair and nails become loose and are easy to remove; the skin begins to split open, exposing muscle and fat" (ibid). The continuation of this process results in the liquefaction of internal organs. Within weeks from onset of death, there is a bloody purge of putrefying liquid from the mouth, nose, anus, or any other opening. Soon afterward, the body bursts open under pressure, spilling its contents. Reeking liquids sink into whatever lies beneath the corpse — be it a casket lining, a mattress, a floor, or soil. Vast quantities of insect larvae may pour out of the body if insects had prior access, and scavengers may pick apart the corpse, which tends to fall apart easily at this stage (Chemistry).

Temperature plays an important role throughout this progression. In warm to moderate climates the body can be reduced to a skeleton within four weeks, while this process can take several months in a cool climate.

Formal Stages of Decomposition

Decomposition begins at the moment of death. In the initial stages it is caused first by autolysis — the breaking down of tissues by the body's own internal chemicals and enzymes — and second by putrefaction, the breakdown of tissues by bacteria. Both processes are responsible for the emission of gases (Decomposition: Free-template).

Historically, a number of stages of the decomposition process have been recognized: autolysis; bloat or putrefaction; decay through putrefaction and carnivore activity; and dry decomposition or diagenesis (Vass A.A. 2001). Modern theoretical approaches tend to divide the process into two central areas: "Current thinking is that it should be segregated into pre- and post-skeletonization since stages are not always observed and in fact may be totally absent, depending on the taphonomy of the corpse" (ibid). In essence, the entire process is summarized as follows: autolysis, putrefaction, and diagenesis together eventually result in complex structures composed of proteins, carbohydrates, sugars, collagen, and lipids returning to their simplest building blocks — essentially dust to dust (ibid).

The following table outlines the formal stages of decomposition.

Table 1. Stages of Decomposition

Initial decay: The cadaver appears fresh externally but is decomposing internally due to the activities of bacteria, protozoa, and nematodes present in the body before death.

Putrefaction: The cadaver is swollen by internally produced gas, takes on a greenish color, and is accompanied by the odor of decaying flesh. The skin may turn greenish or exhibit subcutaneous marbling — the outlines of blood vessels visible beneath the skin.

Temperature, Bacteria, and Chemical Factors

Black putrefaction: The flesh is of a creamy consistency, with exposed parts black in color. The body collapses as gases escape and the odor of decay is very strong.

Butyric fermentation: The cadaver is drying out. Some flesh remains at first and a cheesy odor is present. The ventral surface is moldy from fermentation.

Dry decay: The cadaver is almost dry and the rate of decay is slow. (Source: Majeres, J. 2003)

Numerous factors affect the rate and degree of decomposition over time. Temperature is among the most significant. Its general effect is described as follows: "Approximately 24 hours after death, the corpse usually cools to the ambient temperature. The skin of the head and neck becomes a greenish-red color, and this discoloration spreads to the chest, thighs and entire body over the next several days. Facial features are no longer recognizable and the body begins to smell like rotting meat. This process is accelerated in warm climates and slowed in cold climates" (McLemore, J. 1993).

The rate of decomposition is also largely dependent on temperature, with faster decomposition taking place at higher temperatures. This is an important consideration for forensic medicine, as it can be used to help ascertain the time of death. Determining decomposition rate and time of death depends on a wide array of factors, including not only temperature but also moisture and water. "Individuals submerged in water have different rates of decomposition. Injuries affect the rate as well since damage to the skin increases blood loss, as well as insect and bacterial action" (Vass A.A. 2001). The actions of carnivores will also affect the rate of decomposition.

It is also significant to note that decomposition does not apply only to soft tissue. "A decomposition does not end after the soft tissue has disappeared. The skeleton also has a decompositional rate that is based on the loss of organic (collagen) and inorganic components. Some of the inorganic compounds we use to determine the length of time since death include calcium, potassium and magnesium" (ibid). In a temperate climate, it normally takes ten to twelve years to decompose fully to a skeleton. The high number of variables involved means that exact calculations based on a few characteristics of decomposition are extremely difficult, and all possible decomposition factors must frequently be taken into account.

The role played by microbes and bacteria is extremely significant in the decomposition process, though it is difficult to use as a dependable forensic measurement given the vast number of different bacteria types associated with decomposition. These include Staphylococcus, Candida, Malassezia, Bacillus, and Streptococcus spp., as well as putrefactive anaerobic bacteria (ibid). As one experienced researcher notes, "every micro-organism known is involved in some aspect of the human decomposition cycle from Acetobacter to Zooglea" (ibid). Bacteria can also raise body temperature after death: "In some rare cases, the body temperature has actually increased after death before it cools down. Pathologists accredit this phenomenon partly to bacterial growth that goes unchecked after death" (McLemore, J. 1993).

A noteworthy historical example illustrates how bacteria and insects jointly drive early decomposition. During an exhumation of a soldier buried in the American Civil War, the coffin was opened to reveal a relatively fresh corpse. This was explained by the fact that "prominent soldiers were buried in solid lead coffins — the lead had 'sterilized' the body by poisoning the microflora and decomposition had not progressed past initial autolysis" (Vass A.A. 2001).