Postmortem Changes — Cooling, Lividity, Rigor, Putrefaction and Time Since Death

Postmortem changes are the predictable physical and chemical changes a body goes through after death. Forensic doctors use them for two jobs: to confirm that death has happened and to estimate the time since death (the postmortem interval, PMI). Some of them also hint at the position of the body after death or the cause of death, such as a cherry-red lividity in carbon monoxide poisoning.

Somatic death is the irreversible loss of the vital functions of the brain, heart and lungs — the death of the person as a whole. Individual cells and tissues keep living for a while afterwards; their death (cellular or molecular death) is what drives the early postmortem changes.

Immediately after death the person becomes insensible, voluntary movement stops, and breathing, circulation and nervous function cease. The muscles go into primary relaxation (primary flaccidity), so the jaw drops and the limbs are limp. Within a few minutes the skin turns pale and ashen and loses its elasticity.

• Loss of reflexes — pupillary and corneal reflexes are lost.
• Corneal clouding — the cornea becomes opaque over the following hours.
• Tache noire de la sclérotique — if the eyelids stay open, the exposed sclera dries into a yellowish triangular patch on each side of the cornea. Dust settles on it and it darkens to brown-black.
• Kevorkian sign — fragmentation (segmentation) of the blood column in the retinal vessels, seen with an ophthalmoscope. StatPearls notes its forensic value is limited.

Algor mortis is the postmortem fall in body temperature. Heat production stops at death, and the body loses heat to the surroundings until it reaches ambient temperature. It is one of the earliest and most widely used signs for estimating the PMI.

The fall is not linear. Core temperature first stays almost unchanged for several hours — the postmortem plateau — and then drops steadily over about the next 12 hours, often at 1 to 1.5 °C per hour. Plotted out, the curve is sigmoid (a flipped S, described as a double exponential).

The Henssge nomogram, which corrects for body weight and ambient conditions, is described as the most precise temperature-based method and is most accurate within the first 10 hours. After about 12 hours the margin of error from any temperature method grows large.

Livor mortis — also called postmortem lividity, hypostasis or postmortem staining — is the red-purple discolouration of the dependent parts of the body. Once the heart stops, blood settles under gravity into the lowest vessels. Areas pressed against a surface (shoulder blades, buttocks, calves in a supine body, or under tight clothing) stay pale: this is contact pallor.

Before fixation, turning the body makes the blood drain to the new lowest parts — shifting of lividity. A body with lividity on two opposite surfaces was probably moved after some hours. That is why lividity gives information about body position as well as time.

In living muscle, ATP binds myosin and releases it from actin so the fibre can relax. After death, ATP production stops; when ATP runs out, the actin–myosin cross-bridges cannot detach and the muscle locks rigid — rigor mortis. It resolves later when the muscle proteins break down with autolysis and putrefaction.

Rigor first affects the involuntary muscle of the heart. In skeletal muscle it follows a head-to-foot (cephalocaudal) order: eyelids → neck → lower jaw → chest → upper limbs → abdomen → lower limbs → fingers and toes. It passes off broadly in the same order. Indian textbooks teach this sequence as Nysten's rule.

Cadaveric spasm (instantaneous rigor) is stiffening of a group of muscles that were being used intensely just before death; they become rigid at the moment of death. It follows intense physical or emotional stress just before death — a violent struggle, a suicidal act, drowning — and most often involves the hands: an assailant's clothing or hair gripped in an assault, a weapon in a suicide, or weeds, mud or gravel from the water bed in drowning.

Putrefaction is the breakdown of tissues by bacteria (mainly from the gut) and the body's own enzymes. Its timing depends heavily on temperature, humidity and the cause of death.

1. Greenish discolouration of the right iliac fossa — the first external sign. The skin over the caecum, whose contents are liquid and full of bacteria, turns green as bacterial hydrogen sulphide reacts with haemoglobin to form sulphaemoglobin.
2. Spread of discolouration and marbling — the gas and pigment track along superficial veins, outlining them in a branching pattern called marbling.
3. Gas formation and bloating — the face, abdomen and scrotum swell; purge fluid can leak from the mouth and nose.
4. Skin slippage and blisters, then liquefaction of internal organs.

These are modifications of putrefaction: special conditions change the usual decay and, in the first two, preserve the body's shape for a long time — useful for identification and for finding injuries.

No single sign is reliable on its own. Forensic doctors combine body temperature, lividity, rigor, decomposition, gastric contents, insect evidence and scene findings to give a range, never an exact hour. Temperature methods work best in the first day; decomposition and insect evidence take over later.

• First sign of putrefaction → green discolouration of the right iliac fossa (sulphaemoglobin over the caecum).
• Lividity colour → cherry-red in carbon monoxide; pink in cyanide and cold; brown in nitrite/chlorate poisoning.
• Rigor mechanism → ATP depletion; first in the heart, then eyelids and jaw, last fingers and toes.
• Cadaveric spasm → instantaneous, one muscle group, tells the manner of death.
• Casper's dictum → equal decomposition takes 1 week in air, 2 weeks in water, 8 weeks in soil.
• Adipocere vs mummification vs maceration → wet and warm / dry with warm breeze / dead fetus in utero.
• Lividity vs bruise → incise: blood in vessels that washes off vs extravasated blood that does not.