Decomposition: autolysis and putrefaction
- Finding
After death tissues are broken down by their own enzymes (autolysis) and by bacteria, mostly from the gut (putrefaction).
What it is
Decomposition has two overlapping processes. Autolysis is the breakdown of cells by their own enzymes and starts very early, especially in enzyme-rich organs such as the pancreas, the adrenals and the intestinal mucosa. Putrefaction is breakdown by bacteria, most of them from the gut, which spread through the vessels. The first external sign is usually a greenish patch in the right iliac fossa, where the caecum lies close to the skin, due to sulphaemoglobin formation. Then come venous marbling, blisters and skin slippage, gas bloating and purge fluid from the orifices. The pace depends mainly on temperature: much faster in a hot climate, slower in water and slower still in the ground.
How to tell it apart
- Facial swelling and dark discolouration vs asphyxia or blows: they are decomposition changes if they match the other signs.
- Blood-stained purge fluid vs bleeding from an injury: purge has no bleeding source and no vital reaction.
- Skin slippage vs burn: there is no redness or vital reaction at the edges.
- Internal organs are sometimes better preserved than the surface: autopsy of a decomposed body is still worthwhile.
- Parts of the same body may be at different stages (for example, covered vs exposed areas).
How to recognise it
- Greenish abdominal patch that spreads over the abdomen and then the rest of the body.
- Venous marbling: a branching reddish or greenish pattern on thighs, flanks and shoulders.
- Fluid-filled blisters and sheets of loose epidermis; nails and hair come loose.
- Gas swelling of face, neck, abdomen and genitals; protrusion of eyes and tongue.
- Blood-stained fluid from the orifices and froth at mouth and nose.
How it forms
- Autolysis: the cell's own enzymes destroy it, without bacteria; it underlies early tissue damage.
- Putrefaction: gut bacteria invade tissues and blood after death and produce gases and pigments.
- Haemoglobin is converted into green and brown pigments that stain the skin and vein walls.
- Gas raises abdominal pressure and pushes blood and fluids towards the orifices.
Next step: what to do and document
- Describe decomposition signs with their site and extent, without reading them as injuries.
- Record the temperature and humidity of the place, whether the body was in sun, covered, in water or buried, and any insects.
- Do not conclude a cause of death from the external examination of a decomposed body: a full autopsy is needed.
- Collect insect and fluid samples according to protocol, with chain of custody, if the time since death matters.
- Use personal protection and handle the body with respect; inform the family carefully about visual identification.
Common mistakes
- Reading the blood-stained purge of decomposition as haemorrhage from violence.
- Mistaking venous marbling or the green patch for bruises.
- Giving exact dates from the stage of putrefaction, which depends mostly on temperature.
- Dismissing the autopsy of a decomposed body as useless.
Test yourself
Think of the answer, then tap the question to see it.
Where does the first external sign of putrefaction usually appear, and why?
In the right iliac fossa, because the bacteria-laden caecum lies close to the abdominal wall; green sulphaemoglobin forms there.
What is the difference between autolysis and putrefaction?
Autolysis is breakdown by the cells' own enzymes; putrefaction is breakdown by bacteria, mostly from the gut.
Which factor most affects the speed of putrefaction?
Ambient temperature: heat speeds it up and cold delays or halts it.
What does blood-stained fluid from the mouth and nose of a bloated body usually mean?
It is usually decomposition purge pushed out by gas; on its own it is not a sign of violence.
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Connections
Educational content on forensic and legal medicine; not legal advice and no substitute for the technical guides of Colombia's National Institute of Legal Medicine and Forensic Sciences. Laws change: each page links the official text and says when it was last checked. For a real case, follow the guide in force and ask the competent authority.
Sources: Mummification in a forensic context: an observational study of taphonomic changes and the post-mortem interval in an indoor setting (Ceciliason AS, Käll B, Sandler H) (International Journal of Legal Medicine, 2023); Human Decomposition and Time Since Death: Persistent Challenges and Future Directions of Postmortem Interval Estimation in Forensic Anthropology (Weisensee KE, Atwell MM) (American Journal of Biological Anthropology, 2025); The Minnesota Protocol on the Investigation of Potentially Unlawful Death (2016) (Office of the United Nations High Commissioner for Human Rights, 2017).
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