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Early postmortem changes — livor, rigor and algor mortis
After circulation stops, blood settles into dependent parts (livor mortis), muscles stiffen as ATP runs out (rigor mortis) and the body cools towards ambient temperature — and together the three processes are used to interpret position, circumstances and the time that has passed.
Why it matters in the exam
Exam questions present a body with livor of an unexpected colour or position and ask what it shows. Livor mortis usually appears 20–30 minutes to 2 hours after death, deepens over the following hours and becomes "fixed" — no longer blanching on pressure and no longer shifting when the body is moved — after about 8–12 hours. Livor in two different planes shows that the body was moved after the livor had begun to fix. Areas pressed against a surface stay pale (contact pallor), and in hanging the livor concentrates in the hands, feet and lower limbs.
Colour is a diagnostic clue: cherry-red in carbon monoxide poisoning and in a body kept in the cold, greenish with hydrogen sulphide exposure (sulphaemoglobin), chocolate-brown in methaemoglobinaemia from nitrites and oxidising drugs, and very faint after massive blood loss. Another classic question is distinguishing livor from a subcutaneous bruise: on incision, in livor the blood stays inside the vessels and can be washed away, whereas in a bruise the blood has escaped into the tissue and does not wash out.
Rigor mortis results from actin-myosin bonds that cannot release without ATP. It usually begins 2–4 hours after death, is first noticed in the small muscles of the jaw and face, is complete after 6–12 hours and begins to pass off after 24–36 hours as decomposition starts. Heat, exertion before death and a high body temperature accelerate it; cold delays it. Cadaveric spasm is different: instant stiffening of a group of muscles at the moment of death, rare and of great medicolegal weight. Cooling (algor mortis) begins after a short "plateau", and on average the fall is about 1 to 1.5 degrees per hour, but it depends on clothing, body build, environment and the starting body temperature.
Key points
- Livor: appears within 2 hours, fixes after 8–12 hours and shows whether a body was moved.
- Livor colour: cherry-red in carbon monoxide or cold, brown in methaemoglobinaemia, greenish in hydrogen sulphide.
- Rigor: begins after 2–4 hours, complete at 6–12, passes at 24–36.
- Cooling: roughly 1 to 1.5 degrees per hour, with wide variation.
- Livor washes out on incision; a bruise does not.
Summary table
| Change | When it appears | What it shows | Confounders |
|---|---|---|---|
| Livor mortis | 20–30 minutes to 2 hours; fixed after 8–12 hours | Position, movement of the body, cause-of-death clue from colour | Anaemia and blood loss weaken it; cold alters colour |
| Rigor mortis | 2–4 hours; complete at 6–12; passes at 24–36 | Rough timing, position when stiffening set in | Heat and exertion accelerate; cold delays |
| Cadaveric spasm | At the moment of death | What the deceased gripped at the moment of death | Rare; not to be confused with rigor |
| Algor mortis | After a plateau; about 1 to 1.5 degrees per hour | Time window in the first hours | Clothing, obesity, water, starting temperature |
| Corneal clouding | Hours; faster with open eyes | Supporting sign only | Drying with open eyes (tache noire) |
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Sources
- Knight's Forensic Pathology, 4th edition (2016) — The pathophysiology of death and early postmortem changes
- Simpson's Forensic Medicine, 14th edition (2020) — Changes after death
- Spitz and Fisher's Medicolegal Investigation of Death, 5th edition (2020) — Time of death and changes after death
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.