Fingernails are composed of keratinized tissue, which is naturally translucent and colorless. The healthy pink hue seen in living persons comes entirely from the network of tiny blood vessels, or capillaries, that lie just beneath the nail plate in the nail bed. Once the body’s systems cease to function, this underlying blood supply changes dramatically. This sets off a sequence of visible color alterations that progress over time through biological and chemical events.
Immediate Changes from Lack of Circulation
The first noticeable color change begins within minutes of the heart stopping, driven by the immediate cessation of blood flow. This initial change is known as pallor mortis, or the paleness of death, developing rapidly within 15 to 25 minutes. The capillaries beneath the nail bed lose blood pressure and collapse, draining the oxygenated blood that gives the nails their color.
Following this paleness, a second circulatory change, called livor mortis, becomes visible within the first two hours. Since blood is no longer circulating, gravity pulls the red blood cells downward, causing them to settle in the body’s lowest parts. If the hands are dependent, this pooling of deoxygenated blood in the nail beds causes a reddish-purple or bluish-red discoloration. This post-mortem lividity indicates the position of the body after death.
Specific Discolorations Linked to Cause of Death
The color of the nail beds can provide distinct clues about the systemic condition or toxic agent present at the time of death. These unique shades result from chemical reactions between the circulating blood and specific compounds. A striking cherry-red discoloration is strongly associated with carbon monoxide (CO) poisoning.
Carbon monoxide binds to hemoglobin, forming carboxyhemoglobin, which has a brighter red color than oxygenated hemoglobin. This intense color permeates the tissues, including the nail beds, creating the characteristic cherry-red hue evident after death.
Another distinct color is the brownish or grayish discoloration pointing toward methemoglobinemia, often caused by toxic agents like nitrites. Methemoglobin is an altered form of hemoglobin that cannot effectively transport oxygen. In high concentrations, this altered pigment gives the blood a “chocolate-brown” color, resulting in the blue-grey or grayish appearance of the skin and nail beds. These color shifts reflect chemical changes in the blood that occurred immediately before or at the time of death.
Late-Stage Decompositional Staining
The final color changes occur much later as the body enters the stage of decomposition known as putrefaction. This process is driven by the proliferation of anaerobic bacteria, which normally reside in the gastrointestinal tract. These bacteria begin to break down the body’s tissues, typically starting around four to ten days after death, depending on environmental temperature.
As the bacteria consume tissues, they release gases, including hydrogen sulfide. This gas reacts with the iron released from the breakdown of hemoglobin to form sulfhemoglobin. This reaction results in a progressive greenish-to-black discoloration that spreads across the skin and eventually darkens the nail beds. This deep staining is a sign of advanced decomposition, often coinciding with the loosening and eventual detachment of the nails and hair.