Algor Mortis Definition

Algor Mortis: The second post-mortem indicator of death is Algor Mortis. It is the adjustment of body temperature to the surrounding environment following death.

Humans are among the majority of homeothermic mammals. In other words, unlike “cold-blooded” poikilotherms, we don’t need to lie in the shade when we are too hot or take a sunbath to raise our body temperature. This is due to the fact that homeotherms keep their internal body temperatures consistent.

The average body temperature for an adult is 37 °C (96 °F). The brain-controlled bodily mechanisms take over when the outside temperature poses a threat to the body’s ideal temperature and work to restore equilibrium. We perspire to stay cool when it’s too hot outside (while other animals pant). We shudder, get goosebumps (albeit they don’t do much to warm one up), and huddle up to protect our body heat when it becomes too chilly.

These processes stop functioning after death. The body’s temperature will consequently start to equal the outside temperature. Algor Mortis refers to the alteration in body temperature that occurs after death.

What is Algor Mortis?

The second post-mortem indicator of death is algor mortis. It is the adjustment of body temperature to the surrounding environment. Although this varies based on various environmental factors, it typically takes between 18 and 20 hours for the body temperature to equalise with the ambient temperature if it is below 37°C.

How and why does Algor Mortis occur?

The body’s processes for regulating temperature have malfunctioned, resulting in algor mortis. The central nervous system, the brain, and the circulatory system are some of these mechanisms (primarily).

The circulatory system regulates the body’s temperature. The blood transports heat produced by deeper organs like the muscles or liver to the skin and other outside organs where it can escape. Heat is created by metabolic processes that take place within the body, such as those needed to digest food or move muscles.

the skin’s surface layers. The dermis’s capillary network is shown in the image. (Image courtesy of Madhero88 via Wikimedia Commons)

Under the skin’s epidermis, a network of capillaries exists. Depending on whether heat needs to be released or conserved, these capillaries either dilate (vasodilation) or tighten (vasoconstriction). Depending on the circumstance, the brain gives the circulatory system instructions on how to act.

The skin contains certain receptors that can “feel” temperature. These thermoreceptors provide the brain with a weather report, and the brain bases its executive judgement on this information. The body is incapable of controlling its internal body temperature without the functioning of the brain and heart.

The brain uses more than just changes in blood vessel size to maintain a temperature of 37°C. These strategies increase metabolic reactions in order to produce heat. Shivering is a response to cold weather because it produces heat when muscles move.

The body’s metabolic rate slows down after death. The body is no longer producing any new molecules or energy, yet some metabolic events are still taking place.

The body cannot regulate its temperature if the brain and heart aren’t working. The temperature of the corpse will therefore equalise with the ambient temperature due to the principles of physics. In the first two hours following death, the body temperature will drop by 1°C if it is below 37°C, and it will then continue to drop by 1°C per hour.

Calculating the Time of Death Using Algor Mortis


The period of time between when someone passed away and when their body was discovered is known as the post-mortem interval (PMI). The “time of death” is another name for it. Pathologists and forensic experts give a window of 3 to 4 hours during which the person could have passed away.

Glaister’s equation

Although helpful in calculating PMI, algor mortis isn’t usually the most trustworthy element. A common method used to determine the pace of cooling in the past is the Glaister equation, sometimes known as the “rule of thumb” (when the ambient temperature is less than the body temperature).

Technique of Henssge Nomogram

Another technique for calculating PMI with Algor mortis is the Henssge Nomogram Technique. A nomogram is a visual computation tool. A graph with several parameters exists, and by matching one or more known values, it is possible to use the graph to estimate a third unknown parameter. The rectal temperature and the person’s body weight are taken into account by the Henssge nomogram to calculate the PMI.

Henssge’s nomogram, Nomogramme de Henssge (Image Credit: HB/Wikimedia Commons)

This algorithm should only be used to calculate PMI within the first 18 hours after a person has died. Algor mortis shouldn’t be the only indicator used to calculate PMI, even then. Depending on where in the body the body is, a different rate of cooling (or heating, in rarer circumstances) occurs.

If the body was outside, was it in direct sunshine or shade? Was the deceased dressed, and if so, were the garments ever taken off?

The temperature outside when the body was discovered as well as the temperature during the previous few days are also recorded by forensic professionals in addition to the body temperature.

This can provide forensic professionals with an approximation of the PMI when combined with other gathered evidence (other physiological changes the body goes through, such as rigour mortis and livor mortis, and insects at the places).