The human body goes through various biological processes and changes after death. While the body may appear lifeless shortly after passing, many functions and processes continue for hours or even days afterwards.
What happens immediately after death?
The moment of death is when the heart stops beating and blood circulation halts. Oxygen is no longer delivered to tissues, and carbon dioxide builds up. The lack of oxygen causes brain cells to start dying within 5 minutes. Muscles also become unable to move due to lack of oxygen. However, cells don’t die immediately. Some biological activities can continue in the early stages after death.
How long do the cells stay alive?
At a cellular level, the body does not instantly die at the moment of clinical death. Cells begin to die due to lack of oxygen, but the process can take hours. Muscle cells can take around 2-6 hours to die after oxygen levels drop. Skin cells die within 24-36 hours. Bone cells can survive for several days. Hair follicles and nails can stay alive for several days too. The gut also has some bacterial activity up to 48 hours after death. So while the person has officially died, some cells remain alive and functioning for a period of time.
Autolysis – breakdown of cells
After the heart stops, cells are deprived of oxygen and their membranes break down. This process is known as autolysis or self-digestion. Enzymes contained within the cells are released and start digesting the cells from inside. This begins between 2-6 hours after death. However, because it is such a gradual process, some cells can survive intact for over 24 hours even as other cells around them disintegrate.
Post mortem spasms
The muscles may undergo sudden contractions and spasms after death. This is due to biochemical changes in the muscles. ATP is depleted in the muscles without oxygen, allowing calcium ions to accumulate and cause muscle fibers to contract. These involuntary muscle jerks can occur for hours after death.
Algor mortis – body cooling
When the heart stops, the body loses its ability to regulate temperature. The body cools from its normal temperature of 37°C (98.6°F) and starts approaching the ambient temperature. This process is called algor mortis or death chill. The body loses around 1.5°F during the first hour after death and 1°F every subsequent hour. Factors like body fat percentage, clothes, and air temperature can affect the cooling rate. It usually takes 12-24 hours to reach ambient temperature.
Livor mortis – blood pooling
Once circulation stops, gravity causes the blood to sink down and pool in certain parts of the body. This is known as livor mortis or lividity. The areas touching the ground will appear purplish-red as they become engorged with blood. The process starts 20-30 minutes after death but becomes visible around 2 hours later. The patterns of lividity can give clues about the position of the body after death. Livor mortis usually becomes fixed around 8-12 hours.
Rigor mortis – muscle stiffening
Rigor mortis causes the muscles to stiffen due to chemical changes. It begins around 3-6 hours after death. The small muscles of the face, jaws and neck stiffen first. Over the next 6-12 hours, rigor mortis spreads downwards to the larger muscles of the torso and limbs. It reaches maximum stiffness around 12 hours, then gradually dissipates until 2-3 days when the muscles fully relax again. The rate of onset and resolution of rigor mortis is affected by factors like temperature.
Decomposition
Once the cells begin dying, decomposition of tissues starts. Enzymes from within the body begin breaking down cells and tissues. Bacteria from the gut also start digesting the tissues they can reach. Over time, this leads to discoloration of the skin, bloating of tissues with gas, release of fluids, and breakdown of tissue entirely. However, appreciable decomposition takes longer, around 24 hours after death onwards. The rate of decomposition varies greatly depending on temperature, access by insects, and burial conditions. Mummification can even halt the process almost completely.
Putrefaction
Putrefaction is the decay of proteins by bacteria. Anaerobic bacteria from the gastrointestinal tract start multiplying and digesting tissues after death. They produce gases like hydrogen sulphide, methane, and cadaverine that bloat the body and give off characteristic foul odors. Putrefaction usually begins after around 48 hours. The abdomen discolors first, then the head, neck and limbs as bacteria spread. The gases cause the body to swell. After about 10 days, the organs, muscles and skin rupture, releasing fluids. Putrefaction lasts until the body is skeletonized, which can take weeks or months depending on circumstances.
What are the stages of death?
The events after death occur in a somewhat predictable sequence:
| Time after death | Changes in the body |
| Immediately | Cessation of heartbeat and breathing, loss of consciousness |
| Within minutes | Loss of brain function, pupils dilate |
| 1-6 hours | Cell death, onset of muscle stiffness and paleness |
| 12-24 hours | Cooling to ambient temperature, blood pooling visible |
| 24-72 hours | Maximum rigor mortis, early decomposition |
| 3-5 days | Bloating, marbling and discoloration, active decay |
| 1-3 weeks | Major tissue breakdown, caving in of abdomen |
| 3 weeks – years | Skeletonization, mummification in rare cases |
The duration of each stage depends on conditions like temperature, access to insects, and method of disposal. For instance, refrigeration can significantly delay the process. However, this generalized timeline shows the sequence of changes that occur.
How are the senses affected after death?
While no conscious brain activity exists after death, some reflexes can persist:
Hearing
The ears may still pick up sound at least for a short time after death as the auditory pathways don’t require much oxygen. However, the brain cannot process or respond to the signals so there is no experience of “hearing”.
Sight
The pupils remain reactive to light even hours after death. But there is no visual perception or brain activity associated with sight after passing.
Touch
The skin may still respond to stimuli like temperature, pressure or pain briefly after death. This is due to residual reflex arcs, not sensation.
Smell and taste
Since higher brain function has ceased, the sense of smell does not really persist after death. However, fluids released during decomposition can irritate nasal passages. The mouth also cannot detect tastes without brain input.
So while some reflex actions persist for hours, the brain is unable to sense or perceive anything after death. There is no evidence that any conscious experience continues once the heart stops.
What bodily functions stop after death?
| System | Changes after death |
| Circulatory | Blood circulation and oxygen transport stops |
| Respiratory | Breathing ceases |
| Nervous | All brain function halts |
| Digestive | Food digestion stops but bacterial activity persists |
| Endocrine | Hormones like insulin are no longer regulated |
| Reproductive | Reproductive capabilities are lost |
| Urinary | Kidneys no longer filter blood |
| Immune | No active immune response occurs |
The major measurable sign of death is the end of cardiac and respiratory activity. The brain also stops functioning. Lower systems like the digestive, urinary, and reproductive systems lose regulation and coordination. But some activity in cells and bacteria can persist temporarily.
Conclusion
To summarize, clinical death is marked by the stoppage of heart and lungs. But on a cellular level, some activity and processes can continue from minutes up to days after the heart stops beating. The sequence of events after death follows a somewhat predictable timeline, starting with cell death, followed by muscle stiffening, cooling, and eventual decomposition. While reflexes may persist briefly, all consciousness and brain function ceases permanently once death occurs. The duration of each post mortem change depends on factors like temperature and burial conditions. But eventually, all cells die leaving just the bones and hair. With our current knowledge, there is no evidence that any part of the body or brain remains active and conscious after the person is declared clinically dead.