A dead body doesn’t have one fixed temperature. It starts at living body heat, about 37°C (98.6°F), and slowly drifts toward the temperature of the room, water or ground around it, usually over many hours. So how warm a body feels depends on how long ago death happened and where the body has been. That drift isn’t perfectly steady, which is why even experts treat body temperature as a rough clock rather than an exact one.1PubMed. The evolution of methods for estimating the time of death from body temperature
How a Body Cools After Death
In life, your body holds steady at about 37°C (98.6°F) by burning fuel and adjusting blood flow to the skin. Once the heart stops, both the heat-making and the control end. The body begins losing heat to the cooler air or surfaces around it, a process called algor mortis, Latin for “the chill of death.” The core keeps cooling until it reaches the temperature of its surroundings.
It never goes lower than the room, because heat only flows from warmer things to cooler ones. Once the two match, the body’s temperature simply tracks its surroundings.
In a typical room, a body is often said to lose roughly 0.5 to 1°C (about 1 to 1.5°F) per hour in the early hours, though this varies widely. Most of a day usually passes before it reaches room temperature. The hourly figures are only an average, because cooling follows an S-shaped curve rather than a straight line. The drop is often slow at first, steadier through the middle hours, then slows again near the end. That last slowing happens because heat leaves quickly when the gap between body and room is large and more gradually as the gap closes.
The skin, hands and face cool much faster than the core, so a body can feel cold while the inside is still warm.2PubMed. Modelling postmortem surface cooling in continuously changing environmental temperature Skin is a thin layer pressed against the air and hands off heat quickly, while the deep organs are wrapped in insulating tissue. Hands, feet, nose and ears are small and far from the center, so they are the first places to feel cool.
At a bedside, the hands and feet may feel cool within an hour or two, while the chest and belly stay warm for longer, especially under blankets. A cool hand doesn’t mean the core has reached room temperature.
What Speeds Up or Slows Down Cooling
Body fat under the skin, clothing and blankets all act as insulation and slow cooling.3EBSCOhost. Algor mortis A body under a duvet is surrounded by a trapped layer of warm air, which slows heat loss much as it does for a person sleeping. Fat works the same way from the inside, which is why two people of the same weight but different build can cool differently. Heavier, larger bodies tend to cool more slowly per hour than thin ones.4PubMed. Algor mortis: an erroneous measurement following postmortem refrigeration Wet clothing changes the rate compared with dry clothing.5PubMed. Algor mortis: an erroneous measurement following postmortem refrigeration Water in fabric conducts heat away from the skin far better than dry cloth, and as it evaporates it carries off even more, which is why investigators note wetness.
The surroundings matter just as much. A well-ventilated room cools a body faster than still air, and humid air cools it faster than dry air.6Department of Forensic Medicine, Banaras Hindu University. Postmortem Changes: Algor Mortis and Livor Mortis A body in water cools faster than in air at the same temperature, because water draws heat away more readily.7Department of Forensic Medicine, Banaras Hindu University. Postmortem Changes: Algor Mortis and Livor Mortis Even water at room temperature pulls heat faster than air does. Drownings and bath deaths can therefore cool unusually fast. A body lying on a cold floor also loses heat into it faster than one on a mattress.
The same number of hours after death can give very different temperatures. Removing a blanket, opening a window or moving a body can suddenly speed cooling up, so the history of the room matters as well as its temperature when someone is found.
Heat works the other way. In a hot room or car, a body may barely cool at all. If the surroundings are hotter than 37°C, a body can actually gain heat, and sunlight falling on it adds warmth.
Can a Body Warm Up After Death
Yes, for a while. Soon after death, cells keep breaking down stored sugar, and this releases heat in nearly all bodies.8Wikipedia. Postmortem caloricity In an average adult it can raise temperature by up to 2°C (about 3.6°F).9Wikipedia. Postmortem caloricity Normally this heat is small next to the heat being lost, so it shows up as slower cooling rather than a rise.
Some conditions add more. Infections such as sepsis can add heat as bacteria stay active.10Wikipedia. Postmortem caloricity Heatstroke or certain brain bleeds can leave a body overheated at death.11Wikipedia. Postmortem caloricity Tetanus or strychnine poisoning causes muscle contractions that produce heat.12Wikipedia. Postmortem caloricity In a body like that, the heat produced can outweigh the heat lost for a time.
Warming after death has been linked to intoxication, drug use, brain injury, suffocation, cancer, infection, heart attack and severe agitation before death.13Popular Science. Some corpses may mysteriously heat up after death A body that feels warm hours later isn’t necessarily a sign that death was recent. A person who died with a high fever or heatstroke starts well above 37°C, so the body has farther to fall and can stay noticeably warm for hours with nothing unusual happening afterward. Someone estimating the time of death from temperature alone, assuming a normal starting point, would guess too recent a time.
Finding a loved one still warm to the touch is common. Warmth tells you only that heat is still present, and several ordinary causes can explain it.
Why Cooling Isn’t a Perfect Clock
Sometimes core temperature stays nearly flat for a while after death before it starts dropping. This is called a temperature plateau.14PubMed Central. The post mortem temperature plateau and its role in the estimation of time of death. A review. Whether it appears can’t currently be predicted, because it depends on each person’s state before death, such as fever, drugs or injury.15PubMed Central. The post mortem temperature plateau and its role in the estimation of time of death. A review. The plateau is weaker or absent in the head, including the eye and ear.16PubMed Central. The post mortem temperature plateau and its role in the estimation of time of death. A review.
If the cooling rate is assumed to be steady, a flat early stretch can make a body look as if it died more recently than it did. And since the plateau can’t be predicted ahead of time, a single reading can’t show whether the body is still on it.
Moving a body changes things too. Once it is refrigerated, its temperature says very little about when death happened.17PubMed. Algor mortis: an erroneous measurement following postmortem refrigeration The surroundings change abruptly, the earlier cooling pattern no longer applies, and a later reading mostly reflects the cold storage. That’s why the timing of the move is one of the first questions investigators ask. Bodies moved into cold storage often cool more slowly than math predicts, so experts treat such estimates with great caution.18PubMed. Estimation of time since death after a post-mortem change in ambient temperature: Evaluation of a back-calculation approach
Crime shows tend to give an exact hour. Real estimates are ranges of several hours, and other clues are combined with temperature. Even after about 150 years of study, body temperature still can’t give a precise time of death in real cases.19PubMed. The evolution of methods for estimating the time of death from body temperature
How Experts Measure It
Investigators usually measure core temperature, often rectally, because skin temperature swings with the surroundings.20PubMed. Modelling postmortem surface cooling in continuously changing environmental temperature Forehead and rectal readings both track temperature inside the brain closely.21PubMed. Investigation of post mortem brain, rectal and forehead temperature relations They also record the surrounding temperature, since cooling depends on it.22PubMed. Modelling postmortem surface cooling in continuously changing environmental temperature
At a scene, the order usually runs like this: note the room or outdoor temperature, take the core reading early and before moving the body, then note clothing, coverings, wetness and build. They combine all of it with other signs such as stiffening and skin color changes. Moving a body, lifting off covers or undressing it changes how fast it cools, so the reading is best taken as found.
A widely used chart, the Henssge nomogram, turns one rectal reading into a time estimate right at the scene.23PubMed. Death time estimation in case work. I. The rectal temperature time of death nomogram It takes the rectal temperature, the room temperature and the body weight, and adjusts for clothing and air movement to give a central estimate. Real bodies may not match the average the chart assumes, so the result comes with a margin on either side. Each factor adds uncertainty, which leaves a window often several hours wide. Repeated readings can narrow it.
Temperature methods are most useful in the first hours after death.24Enhanced Knowledge in Sciences and Technology. Post-Mortem Interval Estimation Using Newton’s Law of Cooling and the Henssge Model Most assume steady surroundings, so newer ones try to handle changing temperatures.25undefined. Estimation of the postmortem interval by non-linear programming in conditions of changing ambient temperature
What Happens to Temperature Days Later
Once a body matches its surroundings, its temperature stays there for a while. Then, during decomposition, it rises again, first from bacteria breaking down tissue.26PubMed Central. Temperature and pH dynamics during carcass decomposition and implications for disease management Bacteria from the gut spread through the tissue and give off heat as they work. Later, the activity of masses of maggots becomes the main source of heat.27PubMed Central. Temperature and pH dynamics during carcass decomposition and implications for disease management Their feeding can make a decomposing body warmer than its surroundings days after death. How warm depends on the size of the larval mass and the weather, so there is no single temperature to expect.
Once the body has matched its surroundings, the reading no longer points to a time, and the later rises come from living organisms rather than the original body heat. Experts then rely on insects and other signs instead of cooling.