Eschar is a medical term describing a specific type of tissue that forms following severe injury to the skin and underlying structures. It represents a collection of dead, devitalized tissue that remains attached to the wound bed. Understanding its appearance is important because the visual characteristics of eschar provide immediate information about the severity of the underlying wound. This article will explain what eschar is, how it forms, and detail its specific visual traits.
Defining Eschar and Its Formation
Eschar is fundamentally necrotic tissue that forms due to injury or disease. The process begins when tissue damage causes a severe cessation of blood flow to the area. This loss of circulation, known as ischemia, deprives cells of oxygen and nutrients, leading to rapid cell death. As cells die, the tissue layers desiccate, or dry out, creating a hardened, non-viable layer. This dead material contains dried blood, cellular debris, and proteins. The resulting structure is firmly adhered to the healthy tissue underneath, marking the end stage of tissue necrosis.
The Visual Characteristics of Eschar
Color and Texture
The appearance of eschar is dominated by a distinct change in color and texture. It most commonly presents as black or dark brown, sometimes appearing tan or dark gray. This deep pigmentation results from the breakdown of blood components and the drying of the dead tissue layers. The texture is a defining feature, often described as hard, dry, and leathery. When touched, eschar feels firm and rigid, contrasting sharply with the surrounding pliable skin.
Adherence
This dense, non-pliable nature is a consequence of tissue desiccation and compaction. Eschar is tightly adherent, meaning it is firmly stuck to the underlying wound bed and skin margins. The border between the eschar and viable tissue may show a red or inflamed line of demarcation, indicating the body’s attempt to separate the dead tissue.
Contexts Where Eschar Appears
Eschar in Burns and Pressure Injuries
The precise look of eschar is influenced by the nature of the injury. In severe thermal injuries, such as full-thickness burns, the eschar is often thick, uniform, and very dry. This is due to the extensive damage to all skin layers, which coagulates the tissue into a dense covering. Eschar also commonly appears in advanced-stage pressure injuries, often referred to as bed sores, particularly over bony prominences like the heel or sacrum. Here, the presentation is variable; eschar resulting from chronic ischemia (poor blood flow) is typically dry and hard.
Eschar in Vascular and Infectious Wounds
Conversely, if the underlying dead tissue becomes contaminated with bacteria and moisture accumulates, the eschar may become softer, boggy, or fluid-filled. In wounds related to poor arterial circulation, such as arterial ulcers on the lower extremities, the eschar is usually black and dry due to the severe lack of oxygenated blood supply. Certain infections, like those from specific tick bites or spider bites, can also cause localized tissue necrosis resulting in a smaller, circular patch of eschar. The differing moisture levels and sizes are consequences of the varying depth and cause of the underlying tissue damage.
The Role of Eschar in Wound Assessment
Observing eschar is a significant part of assessing the depth and condition of a wound. Its presence confirms the injury is full-thickness, extending through skin layers and possibly into muscle or bone. Because eschar obscures the wound bed, it prevents clinicians from accurately determining the true stage and extent of the tissue loss beneath it. A crucial distinction is identifying whether the eschar is stable or unstable. Stable eschar is dry, intact, and firmly attached without signs of surrounding redness, swelling, or drainage. In specific locations, such as the heel, stable eschar is sometimes left in place as a natural biological dressing, protecting the compromised tissue underneath. In contrast, unstable eschar is soft, boggy, loose, or accompanied by signs of infection like pus or excessive redness. This presentation suggests that moisture and bacteria are trapped beneath the dead tissue, creating a high-risk environment that often indicates a need for medical intervention.