Lividity, also known as livor mortis or postmortem lividity, is a natural process occurring after death, marking an early sign that circulation has ceased. It involves a discoloration of the skin, typically ranging from pink to a dark purplish hue. This phenomenon provides insights into the post-mortem interval, or time since death. Lividity is a passive change that helps forensic professionals reconstruct aspects of a death scene.
How Lividity Forms and Appears
Lividity forms as blood settles within the body after the heart stops pumping. Once circulation ceases, gravity pulls blood to the lowest, or dependent, parts of the body. This pooling of blood in the capillaries and small vessels causes the reddish-blue or purplish discoloration on the skin. Areas pressed against a hard surface remain pale because pressure obstructs blood from settling, creating “contact pallor” or “blanching.”
The appearance of lividity progresses through distinct stages. It typically begins to be noticeable about 30 minutes to 2 hours after death, appearing as faint red patches. These patches gradually increase in size and intensity, becoming well-formed within approximately 3 to 4 hours. In the initial hours, lividity is considered “unfixed” or “blanchable”; if pressure is applied, the color temporarily fades as blood is pushed away.
Over time, blood cells break down and release hemoglobin, which stains surrounding tissues. This process, known as hemolysis, leads to the “fixation” of lividity. Once fixed, typically around 8 to 12 hours after death, the discoloration will no longer fade when pressure is applied, nor will it shift if the body’s position is changed. This transition from unfixed to fixed lividity is an important indicator for forensic investigations.
Forensic Significance of Lividity
Lividity offers valuable information in forensic investigations, particularly for estimating the post-mortem interval and determining if a body has been moved. The progression from unfixed to fixed lividity helps forensic experts approximate the PMI. If lividity is still blanchable, it suggests death occurred relatively recently, typically within the first few hours. Conversely, if fixed, it indicates a longer post-mortem interval, generally exceeding 8 to 12 hours.
The distribution of lividity provides clues about the body’s position after death. Blood settles in the lowest parts of the body due to gravity at the time of death. If a body is found lying on its back, but lividity is observed on the front of the torso, it suggests the body was moved after death and before lividity became fixed. This inconsistency can be an important piece of evidence in cases involving homicide or body disposal.
While lividity is a useful tool, it is generally used in conjunction with other post-mortem changes, such as rigor mortis (muscle stiffening) and algor mortis (body cooling), for a more comprehensive assessment. Environmental factors, like temperature, and individual characteristics, such as blood volume, can influence lividity’s appearance and timeline. Therefore, forensic professionals consider all available evidence to reconstruct the events surrounding a death.