Postmortem Body Cooling: Algor Mortis Explained

How the Body Cools After Death

Algor mortis (postmortem cooling) is the predictable decline in body temperature toward ambient temperature. It is used in forensic pathology to estimate the postmortem interval (PMI).

Typical Cooling Pattern

• Initial plateau (0.5–1 hour): Temperature may remain stable or even rise slightly due to residual metabolic heat.
• Linear phase (~1–12 hours): Core temperature drops ~1–1.5°C (1.8–2.7°F) per hour under average conditions.
• Asymptotic approach: Cooling slows as body nears ambient temperature; complete equilibration takes 18–24+ hours.

Key Variables Affecting Rate

Factor	Effect on Cooling
Ambient temperature	Lower ambient → faster cooling; higher → slower
Body mass/composition	Higher BMI, more insulation → slower cooling
Clothing/wrapping	Insulates → slows cooling significantly
Air movement/wind	Convection accelerates cooling
Surface contact	Conductive surfaces (metal, wet ground) accelerate cooling
Age/health	Cachexia, low muscle mass → faster cooling
Cause of death	Sepsis, hyperthermia → elevated starting temp; hypothermia → lower

Measurement & Formulas

• Core temperature measured rectally, hepatic, or via abdominal probe
• Common formula (simplified): PMI (hours) ≈ (37°C – measured core temp) / k, where k = cooling constant (typically 0.8–1.2°C/h adjusted for conditions)
• More accurate: Henssge nomogram or finite-element models incorporating all variables

Limitations

• Only reliable in first 12–18 hours
• Highly variable; provides estimate, not exact time
• Must be combined with rigor mortis, livor mortis, entomology, scene context

Algor mortis is a valuable forensic tool when applied with awareness of its many confounders.