Lips turn black (or dark blue/purple) after death primarily due to a lack of oxygen in the blood, a condition known as cyanosis.
Understanding Cyanosis and Post-Mortem Changes
After death, the body's systems cease to function. This includes:
- Cessation of Breathing: Breathing stops, meaning no fresh oxygen enters the lungs.
- Circulatory Shutdown: The heart stops pumping, so blood no longer circulates throughout the body.
Because the blood is no longer being oxygenated, the existing oxygen gradually gets used up by the tissues. Deoxygenated blood is darker in color, appearing bluish or purplish. This discoloration is most visible in areas with thin skin and close proximity to the surface, such as the lips and nail beds.
The Role of Hemoglobin
- Oxygenated Hemoglobin: When hemoglobin (the protein in red blood cells that carries oxygen) is bound to oxygen, it is bright red.
- Deoxygenated Hemoglobin: When hemoglobin releases oxygen, it becomes a darker, bluish-red.
The lips appear black or dark blue/purple because the blood in the capillaries near the surface of the lips is deoxygenated.
Other Post-Mortem Changes Affecting Appearance
While cyanosis is the main reason for the lip discoloration, other post-mortem changes can also contribute to the overall appearance:
- Pallor Mortis: The skin becomes pale due to the cessation of blood circulation. This can make the dark lips appear more prominent.
- Algor Mortis: The body cools down, which can affect blood viscosity and contribute to the overall color changes.
- Livor Mortis (Lividity): Blood settles in the lowest parts of the body due to gravity, causing discoloration. Although this primarily affects larger areas of the body, it can subtly influence the overall coloration.
In summary, the darkening of the lips after death is primarily a result of deoxygenated blood causing cyanosis, exacerbated by other post-mortem changes.
