deteriorate

Corpse in morgue displays signs of Rigor Mortis

The third stage of decomposition known as “Rigor Mortis” translates to “stiffness” [rigor] “of death” [mortis]. The stiffness in a body during the phase of Rigor Mortis is caused by a build up of lactic acid which causes chemical changes within muscles. In life, lactic acid, also known as “milk acid” plays various roles in a body’s biochemical process. The myosin and actin (proteins involved in muscle movement) in the body then begin to harden, causing all muscles in the body to harden for a period of time, as well. At the time of death, “primary flaccidity” occurs and Rigor Mortis begins within 2-6 hours of death, starting with the eyelids, neck and jaw before spreading throughout the rest of the body over the following 4-6 hours. Sometimes all the hardening and contracting of muscles can cause an involuntary postmortem ejaculation in a male corpse. The exact onset and rate of completion of this stage is determined by many factors including age, gender, body type and muscle build; For instance, Rigor Mortis may not be perceivable in infants and children who lack muscle mass. Rigor Mortis may develop more quickly if cause of death is an infection, terminal seizure, electrocution or if the deceased has recently engaged in strenuous exercise or had a higher than average body temperature caused by fever, drugs or intoxication. Generally, 36-48 hours after death “secondary flaccidity” occurs when bacteria in the body begins eating away at the deceased from the inside out, causing the body to end Rigor Mortis and loosen again as muscle tissue begins to deteriorate. Sometimes, it can take 72 hours for the body to reach secondary flaccidity. In a warm environment, Rigor Mortis tends to dissipate sooner than average, whereas in a cold climate, the effects may persist longer.
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Find out what happens prior to Rigor Mortis, Stage 1: Pallor Mortis and Stage 2: Algor Mortis and after Stage 4: Livor Mortis

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Partially skeletonized corpse. Decomposing skin remains in some areas.

The 7th and final stage of decomposition, skeletonization, begins when soft tissue has dried and decayed to the point that parts of the skeleton are visible. Skeletonization is complete once all tissue has decomposed and all that is left of the corpse is bone. Remains may become reduced to bone in as little as three weeks but can take up to several years. Factors including temperature and environment determine the timeline of skeletonization. In a tropical climate the body may be reduced to bone in just a few weeks, in tundra, the process will take several years. Skeletonization may never occur if the corpse is in an environment with persistent subzero temperatures as seen in bodies left behind on Mt. Everest.

Body of George Herbert Leigh Mallory on Mt. Everest. Died on British expedition in 1924. His corpse (discovered May 1,1999) remains in pristine condition to this day due to extreme cold. Photo courtesy Atlas Obscura.

Instead of decomposing, remains of climbers who perished have been preserved due to the extreme cold and now act as trail markers up the treacherous mountainside. The bodies of those who die on Mt. Everest usually remain because an attempt to reach and recover the corpse would most likely prove to be unsuccessful, possibly resulting in another fatality. When the corpse is left in a peat bog or salt desert, skeletonization may be delayed, or natural embalming or spontaneous mummification can occur. The body may saponify, or become “adipocere” if left in certain environments, including a peat bog. This is a rare form of spontaneous mummification seen in the Mutter Museum’s “Soap Lady” who saponified in an alkaline, warm environment which was lacking air. While it is not common, it is possible for a corpse to undergo skeletonization in one area of the body, while experiencing some form of natural preservation in another.

The Soap Lady, who died circa 1830 and was

The Soap Lady saponified, causing the corpse to become a soapy, wax-like substance called adipocere. Photo courtesy of the Mutter Museum.

In an area void of scavenging animals, bodies buried in acidic soil will take approximately 20 years to complete skeletonization and for bone to decompose to the point that practically no evidence of the body is left. In soil with a neutral PH level, a corpse can last as long as 100 years before bone has decayed almost completely. There is also a possibility bone may not deteriorate and the skeleton could instead become a fossil or crude oil.