Lividity (World of Forensic Science)
The term lividity refers to an unnatural color of the skin. Lividity can be a useful reaction in determining the position of a body at the time of death and even whether a body was moved within the first few hours after death.
There are various forms of lividity. In a living person, a blow can result in the localized rupturing of cells and the pooling of blood. When the blood cells begin to decompose, the release of the blood forms a bluish-purple bruise.
In a living victim, bruising can be indicative of the nature of the trauma. For example, choking can leave a distinctive pattern of neck bruising that mirrors the pressure applied by the fingers.
Lividity can also result when blood flow ceases after death. The blood that was formerly flowing through the body can be drawn to the lowest point in the body by the influence of gravity. For example, if a victim was lying on her right side at the time of death, lividity would be evident on the right side of the face, hip, and on the areas of the right arm and leg that were closest to the ground.
As blood pools in a corpse under the influence of gravity, the lividity can become more intense in color. This trend has inspired attempts to correlate the degree of lividity with the approximate time of death. However, the development of lividity is too variable to be an accurate indicator of the time of death. Other indicators, such as rigor mortis, are more reliable.
Movement of a body in the first few hours after death can be evident by patches of lividity on different areas of the body. To continue the example cited above, the right-side pattern of lividity accompanied by a more intense lividity on the lower back and buttocks could indicate movement of the body onto the right side after death.
Typically, postmortem lividity appears as a bluish-purple or reddish-purple color in the regions of the body that are in close contact with the ground. Areas that are further removed from the ground can be pink at the periphery of the discoloration.
Exceptions to these aforementioned colors can be important forensic clues to the cause of death. For example, in carbon monoxide poisoning, lividity can be cherry red in color. When a compound called methaemoglobin forms in the blood, as occurs in exposure to lethal concentrations of potassium chlorate, nitrates, and aniline, lividity tends to be a dark, chocolate-like brown color. Death due to intense cold (hypothermia) or the refrigeration of a recently deceased body will produce a bright pink lividity. The latter color can also be produced if the area of the body was covered by wet clothing.
Lividity typically appears as patches or blotches that coalesce over time to produce a more generalized area of discoloration. After about 12 hours, the lividity becomes fixed. Then, even if the body is shifted, the pattern of discoloration will remain the same.
SEE ALSO Blood; Crime scene investigation; Rigor mortis.