Human blood circulates throughout the body, delivering oxygen, nutrients, and hormones while removing waste products. This fluid also plays a role in immunity and maintaining body temperature. When blood leaves the body and is exposed to the environment, it transforms from a liquid state.
The Common Term for Dried Blood
The most common term for blood that has undergone this transformation is “dried blood.” This phrase accurately conveys its state. When referring to residue left on a surface, “bloodstain” is commonly used to describe the visual mark or discoloration.
A single, universally applied scientific term for dried blood does not exist. However, context often dictates the most appropriate descriptive phrase. In medical or forensic fields, more specific language may be used. For the general public, “dried blood” or “bloodstain” remains the most common and clear descriptor.
The Process of Blood Drying
When blood exits the body, it begins a drying process involving physical and chemical changes. Coagulation begins, forming clots to prevent excessive blood loss. Proteins within the blood plasma convert into fibrin strands, creating a mesh that traps blood cells.
As moisture evaporates, blood components concentrate and solidify. Hemoglobin, the protein in red blood cells responsible for oxygen transport, reacts with oxygen in the air. This oxidation causes the color to shift from bright red to darker hues, ranging from reddish-brown to dark brown or black, much like iron rusts. This interaction of evaporation, coagulation, and oxidation results in a solid, often brittle, residue.
Characteristics and Safety of Dried Blood
Dried blood appears as a reddish-brown to dark brown or black residue, with color varying by age, amount, and surface. Its texture can range from flaky or crusty to powdery. Environmental factors like humidity and surface type can influence its final appearance.
While fresh blood can transmit pathogens, dried blood poses a reduced risk of infection. Most pathogens, including HIV, do not survive long once blood dries and is exposed to air, becoming non-infectious quickly. However, some viruses, such as Hepatitis B and C, can persist in dried blood for longer periods (up to a week for Hepatitis B, several weeks for Hepatitis C).
Despite the lower risk, handle dried blood with care, especially in healthcare or high-risk environments. Proper cleaning practices, including gloves, are recommended for cleanup. For the average person, the risk of infection from dried blood is very low.