Decomposition is the process by which organic matter breaks down after death. For humans, decomposition begins immediately after death and involves the destruction of soft tissue, as the body passes through the sequential stages of autolysis, putrefaction, decay, and skeletonization over a period of weeks, months, or years. The first tissues to visibly decompose are generally the cornea of the eyes, small intestines, and brain. However, decomposition actually starts at the cellular level immediately after death.
What happens when decomposition starts?
Decomposition begins at the moment of death, starting with a process called autolysis. Autolysis occurs when an organism’s digestive enzymes, no longer regulated by the body’s homeostasis mechanisms, begin breaking down cell membranes and tissues. This causes cells to rupture and release their contents into surrounding tissues. The first obvious signs of decomposition include pallor mortis (paleness), algor mortis (cooling of body temperature), rigor mortis (stiffening of muscles), and livor mortis (pooling of blood). Internally, autolysis liquefies organs and tissues through hydrolysis and anaerobic bacterial activity.
The next stage of decomposition is known as putrefaction. This is characterized by the anaerobic bacterial digestion of body tissues, releasing gases that cause bloating of the body and a noticeable odor. Putrefaction is accelerated by the presence of internal body bacteria as well as bacteria from the environment entering orifices and wounds. The gases produced during putrefaction cause the distension of body cavities, forcing fluids out of natural orifices and rupturing skin tissues. This releases strong odors and leads to further insect and animal activity.
What tissue decomposes first in the human body?
The first tissues and organs to visibly decompose in the human body after death are:
- Eyes: The cornea (transparent outer layer of the eye) is typically one of the first tissues to decompose. The cornea does not receive blood supply directly but relies on aqueous humor for nutrition. After death, it swells and becomes hazy within 2-3 days.
- Brain: The brain has high water content and limited structural integrity. It begins decomposing a few days after death. The outer cerebral cortex decays first, before the deeper brain regions.
- Intestines: Digestive enzymes start breaking down the intestinal tissues internally. The small intestine decays faster than the stomach and large intestine.
- Liver: The liver has high metabolic activity and nutrient stores. Autolysis in the cells causes the liver tissue to disintegrate rapidly.
- Lungs: The spongy lung tissue breaks down through autolysis and microbial activity. Decomposition releases carbon dioxide trapped in the lungs.
- Pancreas: Digestive enzymes like amylase and lipase break down the pancreas tissue in autolysis. It liquefies quickly.
The high metabolic activity, moisture content, and warm temperature of these tissues make them ideal sites for early decomposition. They provide favorable conditions for the action of enzymes and bacteria. Tissues with more collagen and structural proteins like skin and tendons remain intact longer than soft tissues.
What factors affect the rate of decomposition?
The main factors that affect the rate of human decomposition include:
- Temperature: Heat speeds up chemical reactions and promotes bacteria growth involved in decomposition. Bodies decompose fastest at temperatures between 70-100°F.
- Access by insects: Insects like blowflies and flesh flies lay eggs in corpses that hatch into larvae (maggots). They accelerate decay of soft tissues.
- Access by scavengers: Scavenging animals like vultures and coyotes shred and consume dead tissues, hastening decomposition.
- Rainfall: In wet conditions, tissue decomposition is faster as moisture promotes bacteria and insect activity.
- Oxygen levels: Aerobic bacteria decomposes tissues faster than anaerobic bacteria. Oxygen availability speeds up decay.
- Fat content: Bodies with more fat decompose slower as fat anaerobically putrefies into adipocere (grave wax).
- Clothing: Tight clothing retains moisture and encourages decomposition while loose clothing allows dehydration.
- Burial: Bodies buried in coffins or in soil without contact of air decompose slower.
External factors like burial depth, coffin material, embalming, and submersion in water also affect the rate of decomposition. Surface decomposition is faster than burial decomposition.
What is the decomposition timeline for a human body?
The approximate timeline for a human body to completely skeletonize is:
| Time after death | Decomposition process |
|---|---|
| Immediately | Pallor mortis, algor mortis, rigor mortis, livor mortis |
| 12-24 hours | Internal autolysis begins |
| 24-72 hours | Distinct odor, bloating and marbling |
| 3-5 days | Purging of decomposition fluids |
| 4-7 days | Peak larval activity by insects |
| 7-10 days | Deflation of body tissues |
| 10-25 days | Advanced decay stage, adipocere formation |
| 3 weeks – 1 year | Skeletonization |
The exact timeline varies greatly based on the environment. In hot and humid climates, skeletonization can occur in weeks while in cold conditions it may take years. Submergence in water also slows decomposition.
What are the stages of human decomposition?
Human decomposition undergoes five main stages:
Fresh stage (0-2 days)
The fresh stage of decomposition occurs during the first few days after death. The body begins cooling to ambient temperature (algor mortis). The pooling of blood due to gravity results in discoloration (livor mortis). Rigor mortis causes stiffening of muscles. Internally, autolysis begins breakdown of cells and tissues by enzymes.
Putrefaction stage (2 days – 1 week)
The putrefaction stage involves anaerobic bacterial decomposition. This produces gases like hydrogen sulfide, methane, cadaverine and putrescine that bloat the body. Tissues begin to liquefy, creating the characteristic fetid odor. Bodies at this stage show marbling and green discoloration.
Black putrefaction stage (1 – 2 weeks)
In the black putrefaction stage, tissues undergo advanced decay. The body deflates due to release of gases. Tissues are sagging and tissues have a black appearance due to accumulation of blood pigments. At this stage, the cadaver is unrecognizable.
Butyric fermentation stage (2 weeks – 1 year)
The butyric fermentation stage produces adipocere (grave wax) through anaerobic conversion of body fat into fatty acids and soaps. This gives the body a wax-like appearance. Mummification can also occur if conditions are very dry.
Skeletonization stage (months – years)
In the final skeletonization stage, all soft tissues are destroyed through autolysis, insect activity, and scavenging. This leaves behind the skeleton, which persists for years until it degrades through weathering.
The duration of each stage depends on the environment. Decomposition occurs faster in warm, moist conditions with insect activity, and slower in cold, dry, or oxygen-depleted conditions.
How does decomposition occur underwater?
The decomposition process is slowed down significantly when a body is submerged in water. The typical stages are:
- Autolysis: Some autolysis occurs, but slower than on land due to lower temperature and oxygen levels.
- Putrefaction: Limited putrefaction occurs. Water prevents insect access and inhibits bacteria.
- Float stage: Gases make the body float to the surface as it decomposes internally.
- Sink stage: After a few weeks, the body absorbs water and sinks as decay proceeds.
- Skeletonization: Aqueous environments dissolve bones over many months.
Submerged bodies decompose about two times slower than on land. Adipocere formation is common, giving the tissues a grey, greasy texture. Aquatic scavengers like fish speed up the process. The depth of water also affects rate of decay.
How does decomposition differ for buried bodies?
Buried bodies decompose slower than exposed bodies due to restricted access by insects, limited oxygen and light exposure, and cooler temperatures. The stages are prolonged:
- Autolysis and putrefaction: Occurs but restricted without oxygen.
- Black putrefaction: Adipocere formation common in moist soil.
- Butyric fermentation: Can proceed over months to years in buried corpses.
- Skeletonization: Bones decompose very slowly over years.
Shallow graves accelerate decomposition while deep graves can mummify bodies. Coffin burial and tight clothing also slow decomposition. Buried bodies decompose in a year while exposed bodies skeletonize in 6-12 months.
How do forensic experts determine time since death?
Forensic experts use the state of decomposition to estimate the post-mortem interval or time since death. Methods include:
- Examination of insect activity and larvae stages
- Studying grave soil chemistry changes
- Observing the level of decay and tissue changes
- Measuring volatile fatty acids released by decay
- Determining degree of skeletonization
- Evaluating adipocere and mummification
Scene context like temperature, burial conditions and submersion also provide clues about decomposition rate and time since death. DNA degradation rates can also indicate post-mortem interval.
How can decomposition be slowed?
Decomposition may be slowed by:
- Keeping the body cool (refrigeration or ice)
- Mummifying the body through desiccation
- Sealing the body in an airtight container
- Embalming to temporarily preserve tissues
- Burying the body deeper underground
- Submerging the body in water or in a sealed body bag
- Wrapping the body tightly to reduce insect access
- Using coffin materials like metal that prevent aerobic decomposition
However, decomposition will eventually occur through autolysis and anaerobic decay. The above methods only delay the process for days to years.
Conclusion
In summary, human decomposition begins immediately after death with autolysis, but the first visible signs appear in the eyes, intestines and brain within 24-72 hours. Putrefaction follows for around a week. Overall time for skeletonization of an exposed body is 6-12 months, while submersion in water or burial can extend the process over years. Understanding the stages and factors affecting the rate of decomposition assists forensic experts in determining time since death.