Livor mortis, or postmortem lividity, is one of the earliest changes seen after death. It is a gravity-dependent discoloration of the skin caused by the pooling of blood after circulation has stopped. This results in a purplish-red or bluish-purple staining on the parts of the body closest to the ground.
The Physical Mechanism of Lividity
Lividity begins immediately when the heart stops pumping and blood flow ceases. The entire volume of blood becomes static, and gravity causes the heaviest components, specifically the red blood cells, to sink through the plasma. These cells accumulate in the capillaries and small vessels (venules) of the tissues nearest the ground, or in the most dependent areas of the body. This congestion of settled, deoxygenated blood beneath the skin causes the characteristic discoloration. Areas pressed tightly against a surface, like the floor or clothing, remain pale because the pressure prevents blood from collecting in those compressed capillaries.
The Standard Timeline: Onset and Fixing
Onset and Blanching
The first signs of lividity can appear quite rapidly, often beginning within 20 to 30 minutes after death. However, this initial onset is often faint and may not be easily visible to the naked eye until about two hours have passed. At this stage, the discoloration is considered “blanchable,” meaning that if pressure is applied to the area, the settled blood is temporarily pushed away, and the color fades.
Fixing
As more time passes, the patches of discoloration increase in size and intensity, reaching their maximum visibility between eight and twelve hours after death. Around this same timeframe, the process of “fixing” begins, which is a significant change in the state of the lividity. Fixing occurs when the red blood cells leak out of the congested vessels and into the surrounding tissues, or when the blood begins to coagulate within the vessels. Once lividity is fixed, the discoloration will no longer disappear or shift when pressure is applied, making it non-blanchable. This fixed state usually occurs after approximately eight to twelve hours and is a strong indicator that the body has been in the same position for a prolonged period during the early post-mortem interval.
Modifying Factors and Appearance
Modifying Factors
Many variables can alter the standard timeline for the onset and fixation of lividity. Environmental temperature is one of the most powerful modifiers, as warmer conditions generally speed up the process while colder conditions slow the movement of blood cells. The individual’s underlying health conditions also play a role; for example, a person with severe anemia may exhibit less visible lividity due to a lower overall red blood cell count.
Color and Forensic Significance
The color of the lividity can also be affected by the circumstances of death, providing clues about the cause. Lividity is typically a purplish-blue hue because the settled blood is deoxygenated, but certain poisons cause distinct color shifts. A bright cherry-red color, for instance, is often seen in cases of carbon monoxide poisoning because the gas binds tightly to hemoglobin, keeping the blood oxygenated and bright. Pinker hues may be associated with certain conditions like hypothermia or cyanide poisoning. The pattern of the fixed lividity is a valuable piece of information for investigators. By observing the location of the discoloration, it is possible to determine the position of the body when the blood settled. If lividity is found on the back, but the body is discovered lying face down, it confirms the body was moved after fixation.