Lividity, scientifically known as livor mortis or post-mortem hypostasis, is one of the earliest physical changes observed after death. It is a visible discoloration of the skin caused by the pooling of blood in the lowest parts of the body due to gravity once the heart ceases to pump. The appearance and progression of this staining provide valuable information regarding the circumstances and timing of death.
The Mechanism of Livor Mortis Formation
Lividity begins the moment circulation comes to a complete halt. Without the heart’s continuous action, gravity immediately acts upon the blood. The blood vessels, particularly the small capillaries and venules, lose their muscle tone in a state known as post-mortem vasodilation. This relaxation allows the blood to passively drain into the vessels of the body parts closest to the ground.
Denser red blood cells settle out and accumulate in these dependent areas, causing the skin to become visibly discolored. Areas pressed against a firm surface, such as a floor or a bed, remain pale because the capillaries are compressed, preventing blood from settling there. This creates characteristic pale patches known as contact pallor, contrasting sharply with the surrounding stained skin.
Observable Characteristics and Timeline
Lividity typically presents as a reddish-purple or bluish-purple discoloration of the skin. The specific color is determined by the oxygen saturation of the pooled blood’s hemoglobin. Discoloration usually begins to appear as small patches within 30 minutes to two hours following death, and the patches coalesce into larger, more widespread areas over the next few hours.
Blanchable Lividity
During this early phase, the lividity is described as “blanchable.” If pressure is applied to the discolored skin, the blood is temporarily pushed out of the capillaries, and the area turns pale. Variations in color can offer clues about the cause of death. For instance, a bright cherry-red discoloration is commonly observed in cases of carbon monoxide poisoning, while cyanide poisoning may result in a brick-red color.
Fixed Lividity
The most significant transition occurs when the lividity becomes “fixed,” typically between eight and twelve hours post-mortem. Once fixed, applying pressure no longer causes the discoloration to blanch or fade. This fixation results from two concurrent processes: the blood begins to coagulate within the vessels, and red blood cells undergo hemolysis, releasing hemoglobin that stains the surrounding tissues.
Forensic Application in Death Investigation
The progression of lividity is a valuable tool for medical examiners and death investigators, offering two main areas of insight.
Determining Body Position
The first application is determining the position of the body during the initial hours after death. The pattern of staining directly corresponds to the body’s orientation relative to gravity when the blood settled. For example, fixed lividity across the back of a face-down body indicates the individual died on their back and was moved after fixation. If the body is moved before fixation, the blood shifts to the new dependent areas, forming a secondary pattern of lividity.
Estimating Time Since Death
The second application involves estimating the post-mortem interval (time since death). The state of lividity—whether it is blanchable or fixed—provides a rough window of time. While the timeline is subject to various factors like ambient temperature and blood volume, the transition from blanchable to fixed lividity offers a tangible physical marker. Investigators use the timeframes associated with blanching and fixation to establish a time frame for death, which is then used in conjunction with other post-mortem markers, like rigor mortis, for a more accurate estimate.