Knife After Death

5 Main Stages of Decomposition

Intro to the stages of human decomposition

Forensic Pathologist/Medical Examiners often have to perform autopsies on bodies in various stages of decomposition. There are five stages of human body decomposition, each with different characteristics. These stages are determined by the amount of time since death and environmental factors of a dead body. The stages of decomposition include:

stages of decomposition
Stages of Decomposition (Photo Credit BioSoCal)

1. Initial Breakdown

Human body temperature starts cooling as soon as the death occurs. This is known as algor mortis. Without oxygenated blood flow, muscular tissues become rigid with a lack of movement. Rigor mortis is the stiffening of the muscles and joints a few hours after death and can last one to four days, depending on the activities and health before death and the environmental conditions.

Once bacteria start digesting what they find inside intestines— cells of human remains lose structural integrity along with proteins & lipids while also breaking down carbohydrates. At the end of this stage, insect activity may begin, most commonly flies will lay eggs which will eventually become maggots.

2. Bloating

Bloating occurs a short time after death.  As bacteria grow and reproduce, they produce gasses that may cause bloating or push fluids out of the body. These gasses include methane, carbon dioxide, nitrogen, and hydrogen sulfide. Some of these sulfurous compounds can attract flies to lay eggs and produce maggots (also known as “fly larvae”) that feed on dead tissue. This results in steady consumption of bodily tissues.  Skin slippage and bullae (fluid-filled blister) formation may also begin to occur.

Livor mortis refers to the pooling of blood within the body after death. When blood no longer circulates and blood pressure drops to zero, gravity is the predominant force on the blood within vessels. This causes it to settle in the dependent (gravity-dependent) parts of the body. In a body that is lying supine (face up), blood will collect at the back of the head, the back, and posterior portions of the arms and legs. Livor mortis very often has a pinkish-purple color.

3. Active Decay

It’s during the active decaying process that most body mass is lost due to bacteria and insects processing the body material along with liquids being released into the surrounding environment. During this stage, the area of decomposition expands into the surroundings and most insects are present while they feed on bodily fluids. In addition, a body left in the outside environment may undergo anthropophagy, which is when animals may investigate the body, even consuming portions of it. The weather conditions such as increased temperature, humidity, and precipitation may accelerate decomposition.

4. Advanced Decay

By this point, most soft tissues have decomposed and only bones, hair, and tendons/ligaments may remain. This process is more likely to proceed quickly if a body is outdoors and exposed to the elements, particularly in warm and wet environments. When a body is indoors, one may see mummification, in which the body’s soft tissues are not completely consumed, but rather become very dehydrated and shrunken. The soft tissue that does remain is leathery, darkened, and closely approximates the remaining bony structures.

5. Skeletonization

The last stage refers to when only bones and scant connective tissue elements remain. The actions of animals and insects have often defleshed the body by this point. Exposed to the elements, the bones may lighten in color and if outside, maybe eventually reclaimed by the earth or scattered by the action of animals.

Skeletonization stage of human decomposition.
Skeletonization stage (Photo Credit Science Focus)

How quickly a body decomposes

Bodies decompose at different speeds depending on the surrounding environment they are exposed to. A body left in an exposed, warm place will break down much faster than a body buried or confined indoors with no airflow around them–and similarly for cold temperatures! To give an example, a body may be quickly defleshed in a warm, humid environment with abundant animal and insect activity, some described examples in the literature indicate less than 2 weeks. However, in cold environments, very little decomposition will occur, even in outdoor environments.

Summary of the Stages of Decomposition

Decomposition is nature’s way of recycling. When decomposition occurs, bodies release their nutrients back into the earth, into insects and animals so new growth will once again occur. It is in a way, a form of homeostasis in nature.

In summary, the five stages of the decomposition process are initial breakdown, bloating, active decay, advanced decay, and skeletonization. How rapidly a body decomposes depends on location, temperature, and whether or not other scavenging life forms are present.