Final answer:
An eschar is a dried mass of dead tissue on the skin often associated with severe infections such as necrotizing fasciitis, which is characterized by potentially life-threatening tissue death and requires prompt medical attention.
Step-by-step explanation:
Dried serum blood or purulent exudate on the skin is commonly referred to as an eschar. This term describes a localized mass of dead tissue that has dried and adhered to the skin surface. It is often associated with certain skin infections, burn wounds, or necrotic tissue resulting from an underlying infection like necrotizing fasciitis. In the context of infection, eschars can be a sign of severe infection where there is tissue death, such as an area with necrotizing fasciitis. A classic symptom of this condition is a rapidly spreading rash, accompanied by bullae formation (fluid- or pus-filled bumps on the skin) and skin discoloration. If left untreated, infections associated with eschar formation can be life-threatening, which is why medical attention is crucial for patients with these symptoms.