Lividity, scientifically known as livor mortis, is one of the three classic post-mortem signs, alongside rigor mortis and algor mortis. It is characterized by a purplish-red or reddish-blue discoloration of the skin resulting from blood pooling within the body’s vessels. This appearance is a direct consequence of the cessation of circulation, indicating that death has occurred. The discoloration becomes observable on the lowest, or most dependent, areas of the body due to gravity.
The Biological Mechanism of Lividity
The formation of lividity is a passive process that begins the moment the heart stops pumping blood. Blood is no longer actively circulated and begins to settle in the body’s smallest blood vessels, the capillaries and venules, in the areas closest to the ground. This gravitational settling occurs because the vessel walls lose their tone, allowing heavy red blood cells (erythrocytes) to sink through the lighter serum. The accumulation of deoxygenated blood in the superficial capillary network produces the characteristic purplish-red discoloration visible through the skin.
The final color of the lividity can offer clues about the environment or the cause of death by reflecting the oxygenation level of the pooled blood. Typically, the color is purplish-red due to the presence of reduced, deoxygenated hemoglobin. However, an unusually bright, cherry-red or pink lividity is a significant forensic indicator, often associated with carbon monoxide poisoning. In these cases, carbon monoxide binds tightly to hemoglobin, forming carboxyhemoglobin, which retains a bright red color. Other atypical colors include brick red from cyanide poisoning or bronze from certain septic deaths.
Development and Fixation Timeline
Lividity follows a predictable progression used by forensic experts. The onset of lividity, where faint patches of discoloration first become noticeable, typically begins between 20 minutes and three hours after death. These initial patches gradually increase in size and intensity, eventually merging to form larger, uniformly stained areas in the dependent regions of the body.
During the early hours following onset, the pooled blood remains fluid within the vessels, meaning the lividity is considered non-fixed or blanchable. Applying pressure to the discolored area, such as with a fingertip, will temporarily push the blood out of the capillaries, causing the skin to turn white, or “blanch”. When the pressure is released, the color quickly returns as the blood flows back into the vessels.
The transition to fixed lividity is a significant marker in the post-mortem timeline. Fixation occurs when the pooled blood within the vessels begins to clot and red blood cells start to break down (hemolysis), allowing hemoglobin to diffuse into the surrounding tissues. Once this process is complete, applying pressure to the area will no longer cause the discoloration to disappear. Lividity is typically fully fixed between eight and twelve hours after death.
Using Lividity in Forensic Investigations
Lividity’s development and fixation make it a valuable tool in forensic investigations, primarily for estimating the time of death and detecting body movement. By observing whether the lividity is still blanchable (non-fixed) or non-blanchable (fixed), investigators establish an initial time window for the post-mortem interval (PMI). For example, finding a body with non-fixed lividity suggests death occurred less than eight hours before the examination.
The distribution of fixed lividity is especially useful for determining the position of the body at the time of death and whether it was moved afterward. Lividity forms only on the surfaces closest to the ground; areas of the skin compressed against a hard surface, like a floor or a belt, will remain pale, creating patterns of contact pallor. If a body is found lying face up, but the lividity is fixed on the front of the torso, it indicates the body was in a face-down position for a prolonged period before being moved.
This contradiction between the body’s found position and the location of fixed lividity indicates that the body was repositioned after fixation occurred. Observing these patterns allows investigators to challenge or corroborate witness statements about the circumstances of the death. Lividity provides a physical record of the body’s position during the early hours after death, offering clues about the sequence of events at a crime scene.