Decomposition is the process in which the
organs
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...
and
complex molecules of
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
and
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
bodies break down into simple
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
over time. In
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s, five stages of decomposition are typically recognized: fresh, bloat, active decay, advanced decay, and dry/skeletonized.
Knowing the different stages of decomposition can help investigators in determining the
Post Mortem Interval
The post-mortem interval (PMI) is the time that has elapsed since an individual's death. When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can ra ...
(PMI).
The rate of decomposition of human remains can vary due to environmental factors and other factors.
Environmental factors include
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
, burning,
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
, and the availability of oxygen.
Other factors include body size, clothing, and the
cause of death
In law, medicine, and statistics, cause of death is an official determination of conditions resulting in a human's death, which may be recorded on a death certificate. A cause of death is determined by a medical examiner. The cause of death is ...
.
Stages and characteristics
The five stages of decomposition—fresh (aka autolysis), bloat, active decay, advanced decay, and dry/skeletonized—have specific characteristics that are used to identify which stage the remains are in. These stages are illustrated by reference to an experimental study of the decay of a pig corpse.
Fresh
At this stage the remains are usually intact and free of insects. The corpse progresses through
algor mortis
Algor mortis (Latin: ''algor''—coldness; ''mortis''—of death), the second stage of death, is the change in body temperature post mortem, until the ambient temperature is matched. This is generally a steady decline, although if the ambient t ...
(a reduction in body temperature until
ambient temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
is reached),
rigor mortis
Rigor mortis (Latin: ''rigor'' "stiffness", and ''mortis'' "of death"), or postmortem rigidity, is the third stage of death. It is one of the recognizable signs of death, characterized by stiffening of the limbs of the corpse caused by chemic ...
(the temporary stiffening of the limbs due to chemical changes in the muscles), and
livor mortis
Livor mortis (Latin: ''līvor'' – "bluish color, bruise", ''mortis'' – "of death"), postmortem lividity (Latin: ''postmortem'' – "after death", ''lividity'' – "black and blue"), hypostasis (Greek: ὑπό, ''hypo'', meaning "under, bene ...
(pooling of the blood on the side of the body that is closest to the ground).
Bloat
![Example of a pig carcass in the bloat stage of decomposition](https://upload.wikimedia.org/wikipedia/commons/f/f5/Example_of_a_pig_carcass_in_the_bloat_stage_of_decomposition.jpg)
At this stage, the
microorganisms residing in the human gut begin to digest the tissues of the body, excreting gases that cause the torso and limbs to bloat, and producing foul-smelling chemicals including
putrescine
Putrescine is an organic compound with the formula (CH2)4(NH2)2. It is a colorless solid that melts near room temperature. It is classified as a diamine. Together with cadaverine, it is largely responsible for the foul odor of putrefying flesh, b ...
and
cadaverine
Cadaverine is an organic compound with the formula (CH2)5(NH2)2. Classified as diamine, it is a colorless liquid with an unpleasant odor. It is present in small quantities in living organisms but is often associated with the putrefaction of anim ...
.
Cells
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
in tissues break down and release
hydrolytic enzyme
Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...
s, and the top layer of skin may become loosened, leading to skin slippage.
Decomposition of the gastrointestinal tract results in a dark, foul-smelling liquid called "purge fluid" that is forced out of the nose and mouth due to gas pressure in the intestine.
The bloat stage is characterized by a shift in the bacterial population from
aerobic
Aerobic means "requiring air," in which "air" usually means oxygen.
Aerobic may also refer to
* Aerobic exercise, prolonged exercise of moderate intensity
* Aerobics, a form of aerobic exercise
* Aerobic respiration, the aerobic process of cellu ...
to
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
bacterial species.
Active decay
![Example of a pig carcass in the active decay stage of decomposition](https://upload.wikimedia.org/wikipedia/commons/c/ce/Example_of_a_pig_carcass_in_the_active_decay_stage_of_decomposition.jpg)
At this stage, the tissues begin to liquefy and the skin will start to blacken.
Blowflies
The Calliphoridae (commonly known as blow flies, blow-flies, carrion flies, bluebottles, greenbottles, or cluster flies) are a family of insects in the order Diptera, with almost 1,900 known species. The maggot larvae, often used as fishing b ...
target decomposing corpses early on, using specialized smell receptors, and lay their eggs in orifices and open wounds.
The size and development stage of
maggot
A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies.
...
s can be used to give a measure of the minimum time since death.
Insect activity occurs in a series of waves, and identifying the insects present can give additional information on the
postmortem interval
The post-mortem interval (PMI) is the time that has elapsed since an individual's death. When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can ra ...
.
Adipocere
Adipocere (), also known as corpse wax, grave wax or mortuary wax, is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses. In its formation, putrefaction is replaced by a permanent ...
, or corpse wax, may be formed, inhibiting further decomposition.
Advanced decay
During advanced decay, most of the remains have discolored and often blackened.
Putrefaction
Putrefaction is the fifth stage of death, following pallor mortis, algor mortis, rigor mortis, and livor mortis. This process references the breaking down of a body of an animal, such as a human, post-mortem. In broad terms, it can be viewed ...
, in which tissues and cells break down and liquidize as the body decays, will be almost complete.
A decomposing human body in the earth will eventually release approximately 32g of nitrogen, 10g of phosphorus, 4g of potassium, and 1g of magnesium for every kilogram of dry body mass, making changes in the chemistry of the soil around it that may persist for years.
Dry/skeletonized remains
Once bloating has ceased, the soft tissue of remains typically collapses in on itself. At the end of active decay, the remains are often dried out and begin to
skeletonize.
Environmental factors
Temperature
The climate and temperature in which a corpse decomposes can have great effect on the rate of decomposition.
Higher temperatures will speed up the rate of decomposition as it accelerates the physiological reactions in the body after death.
Cooler temperatures will slow the rate of decomposition.
Sunlight availability will also influence the temperature and, as a result, influence decomposition.
When there is more sunlight available this will facilitate decomposition whereas shaded areas can slow down decomposition.
Humidity
The amount of moisture in the environment in which a corpse decomposes also has an effect on the rate of decomposition.
Humid environments will speed up the rate of decomposition and will influence
adipocere
Adipocere (), also known as corpse wax, grave wax or mortuary wax, is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses. In its formation, putrefaction is replaced by a permanent ...
formation.
In contrast, more arid environments will dry up faster but will overall decompose more slowly.
Oxygen Availability
Whether the corpse is in a more anaerobic or aerobic environment will also influence the rate of decomposition.
The more oxygen there is available the more rapid decomposition will take place.
This is because the
microorganisms
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
required for decomposition require oxygen to live and thus facilitate decomposition.
Lower oxygen levels will have the opposite effect.
Burial
Burial
Burial, also known as interment or inhumation, is a method of final disposition whereby a dead body is placed into the ground, sometimes with objects. This is usually accomplished by excavating a pit or trench, placing the deceased and objec ...
postpones the rate of decomposition, in part because even a few inches of soil covering the corpse will prevent blowflies from laying their eggs on the corpse. The depth of burial will influence the rate of decomposition as it will deter
decomposers
Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that they use ...
such as scavengers and insects.
This will also lower the available oxygen and impede decomposition as it will limit the function of microorganisms.
The pH of the soil will also be a factor when it comes the rate of decomposition, as it influences the types of decomposers. Moisture in soil will also slow down decomposition as it facilitates anaerobic metabolism.
Wet environments
Submersion in water typically slows decomposition. The rate of loss of heat is higher in water and the progression through
algor mortis
Algor mortis (Latin: ''algor''—coldness; ''mortis''—of death), the second stage of death, is the change in body temperature post mortem, until the ambient temperature is matched. This is generally a steady decline, although if the ambient t ...
is therefore faster. Cool temperatures slow bacterial growth. Once bloat begins, the body will typically float to the surface and become exposed to flies. Scavengers in the water, which vary with the location, also contribute to decay. Factors affecting decomposition include water depth, temperature, tides, currents, seasons, dissolved oxygen, geology, acidity, salinity, sedimentation, and insect and scavenging activity. Human remains found in aquatic surroundings are often incomplete and poorly preserved, making investigating the circumstances of death much more difficult.
Other factors
Body Size
Body size is an important factor that will also influence the rate of decomposition.
A larger body mass and more
fat
In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food.
The term often refers spec ...
will decompose more rapidly.
This is because after death, fats will liquify, accounting for a large portion of decomposition.
People with a lower fat percentage will decompose more slowly.
This includes smaller adults and especially children.
Clothing
Clothing and other types of coverings affect the rate of decomposition because it limits the body's exposure to external factors such as weathering and soil.
It slows decomposition by delaying scavenging by animals.
However, insect activity would increase since the wrapping will harbor more heat and protection from the sun, providing an ideal environment for maggot growth which facilitates organic decay.
Cause of Death
The cause of death can also influence the rate of decomposition, mainly by speeding it up.
Fatal wounds like stab wounds or other lacerations on the body attract insects as it provides a good spot to oviposit and, as a result, could increase the rate of decomposition.
Experimental analysis of decomposition on corpse farms
Corpse farms are used to study the decay of the human body and to gain insight into how environmental and endogenous factors affect progression through the stages of decomposition.
In summer, high temperatures can accelerate the stages of decomposition: heat encourages the breakdown of organic material, and bacteria also grow faster in a warm environment, accelerating bacterial digestion of tissue. However, natural
mummification
A mummy is a dead human or an animal whose soft tissues and organs have been preserved by either intentional or accidental exposure to chemicals, extreme cold, very low humidity, or lack of air, so that the recovered body does not decay furth ...
, normally thought of as a consequence of
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
conditions, can occur if the remains are exposed to intense sunlight. In winter, not all bodies go through the bloat stage. Bacterial growth is much reduced at temperatures below 4 °C.
Corpse farms are also used to study the interactions of insects with decaying bodies.
References
{{Reflist
Medical aspects of death