Tissue Types

The integumentary system, or skin (and its associated structures), is the largest organ of the human body and primarily serves as a physical barrier between the external and internal environments (Marieb & Hoehn, 2010). As the human body’s primary method of protection, the skin’s associated structures work to maintain a surface pH of 4.1 to 5.8 (Lukić et al., 2021) to stave off excess surface bacteria. In addition to impeding infectious pathogens, the skin also provides us with sensation, regulates our body temperature, and synthesizes Vitamin D. It is essential for anyone involved in any method of debridement to identify anatomical structures and know physiological processes of the skin and that which lay beneath it, as unintentional injury to structures such as muscle, tendons, and nerves may result in potential loss of function.

Assessing the process of tissue death can help the clinician determine what tissue(s) may need debriding. It is equally important for anyone authorizing or performing debridement to be able to accurately identify and separate healthy tissue from nonviable tissue. There are many different types of tissue, and within each type there may be further categories. Accurate identification of the wound bed is necessary to anticipate healing time, risk of infection (Grey et al., 2006), and develop safe and appropriate care plans. Note: Tissues and underlying structures must remain moist to maintain viability.

Preview the slideshow of various skin and tissue types. This is a collection of images ranging from normal to abnormal tissue types: healthy pink granulation tissue, different types of necrotic tissue (black, dry eschar) including yellow slough on the wound bed surface and exposed underlying structures including bone and tendon.


Epithelial tissue, or epithelium, covers the body’s surface and provides boundaries between the internal and external environments (Marieb & Hoehn, 2010). Functions include protecting the surface of the wound from infective pathogens and further injury (Alhajj et al., 2020). Tissue colour can be pale pink/white islands within the wound bed in partial thickness or advancing border in full thickness wounds. Management of epithelial tissue requires protection and maintenance of adequate hydration. Observing epithelial cells at the wound edges can provide information about the quality of the wound bed. An advancing border usually indicates a reasonably healthy wound bed whereas rolled wound edges (epibole) or unattached edges indicate something is amiss and consultation with the wound specialist and interprofessional team is warranted.

Granulation tissue is required for wounds to heal by secondary intention as new blood vessels develop to form connective tissue which fills the wound during the proliferative stage of healing. Healthy granulation tissue is moist and pink to red in colour (Figure 2). Formation of healthy granulation tissue requires enough circulation to carry oxygen and nutrients to the wound bed. If circulation is significantly impaired, or when underlying comorbidities, such as low hemoglobin are present, the granulation tissue may be pale pink (Figure 3). Unhealthy granulation tissue may appear dark or dusky in colour and bleed easily (Wound Source, 2021). In some instances, excess granulation may develop called hypergranulation tissue. This unhealthy tissue is often due to excess moisture or rising bacterial levels and should cue the health care professional to reassess the plan of care to treat the underlying cause. In fact, any tissue above the level of skin should be referred to a wound specialist (defined below).

Adipose tissue, or fat, is most often found in the subcutaneous layer of skin and is usually yellowish/white in colour (except for newborns when it is brown) and globular. It provides the body with insulation and cushioning and contains various structures including blood vessels, nerves, and lymphatic vessels (Albaugh & Loehne, 2010). The colour will change to a darker yellow if adipose tissue becomes damaged (Figure 4).

Fat pads located in the feet, often can be confused with slough therefore accurate identification of the underlying structure is imperative, especially prior to debridement.

Muscle supports the skeletal structure to enable functional body movement. Healthy striated muscle is bright red in appearance (Figure 5) related to the abundance of vasculature throughout and has a firm, rebound feel on palpation (Albaugh & Loehne, 2010). Asking the patient to contract the muscle in and around the wound can confirm muscle is in fact exposed. Like fascia, healthy muscle can be inappropriately identified as granulation tissue, when assessed by someone without advanced education and preceptorship in wound management, increasing the risk of significant harm and unintentional debridement.

Fascia is a dense connective tissue adjoining muscle and organs and can be found directly beneath the subcutaneous layer. It provides support for skin, muscles, tendons, organs, and ligaments by providing shape and reducing friction during movement. It is primarily collagen and therefore is shiny and white in colour and often appears as fibrinous bands or sheath (Figure 6). Unintentional debridement of fascia significantly increases the risk of infection, as microbes spread easily along this tissue type (Albaugh & Loehne, 2010), and creates friction in areas where there should be no friction such as between muscle and other organs or structures. Fascia can very easily be mistaken as fibrinous tissue or slough (Figures 5 and 6) by an untrained or novice eye and therefore should be managed in consultation with a wound specialist and collaboration with the interprofessional team.

Tendon or ligament is a tough band of tissue that connects two other tissues together (i.e., bone to muscle or bone to bone, respectively). Its colour can range from white to yellow depending on the level of hydration. Healthy tendons are shiny and white (Figure 7). When damaged, or dehydrated, it darkens to a yellowish colour as it begins to die. Therefore, maintaining moisture in tendons is crucial. Tendons can be located very close to the skin’s surface in some areas (Figure 8) and are commonly damaged during sharp debridement by a self-taught or self-educated health care professional (Harris, 2009). Like muscle, when asking the patient to move the associated limb the tendon can be seen to contract in the wound bed.  

Nerves are grayish-white in colour and located within the subcutaneous tissue layer placing them at high risk for unintentional injury. Nerves are required for internal communication and motor function, so when cut or damaged, muscle and motor function fails, and touch sensation is lost.

Bone is white or pale yellow (Figure 3) and hard on palpation, when healthy. Bone is often missed in the visual assessment therefore palpating with a gloved finger or gently probing the wound base with the wooden end of a cotton tipped applicator stick to confirm the hard bone confirmation. When a patient’s wound reveals exposed bone and infection is suspected, especially in diabetic foot ulcers, a referral for further evaluation and treatment to a wound care team may be needed for consideration of systemic antibiotics. Management includes promoting the growth of granulation tissue and maintaining a moist and clean environment to prevent infection (Young, 2015). Only specially trained health care professionals with surgical skills including surgeons and podiatrists should be debriding bone.

Blood vessels are found throughout the body and include both the arterial and venous systems. Knowing the anatomy of the vascular system is extremely important as wounds can develop in areas over large arteries making debridement risky. Wounds located over major arteries should not be debrided outside of a well-controlled setting with access to appropriate resources including a vascular surgeon.


Types of Necrotic Tissue

Nonviable tissue is a term used collectively to describe different types of necrotic tissue. Necrotic tissue can be any tissue that is no longer viable due to inadequate blood supply. When necrotic tissue hardens and becomes black, it is referred to as hard black eschar (Figure 9), and as autolysis occurs the texture and colour changes and it becomes a soft brown eschar (Figure 10), then further transitions to adherent grey/yellow slough (Figure 11) and loosely adherent slough (Figure 12).

Eschar, black and brown, and can be hard/dry or soft/wet. If the wound is determined to be healable, debridement may be indicated (refer to Chapter 1 for descriptions of healabIe, nonhealable) if the wound is considered nonhealing or nonhealable, debridement may be contraindicated and therefore the best method of management includes painting the wound and periwound skin with povidone iodine and covering it with a dry gauze-based dressing. Inappropriate debridement of stable eschar, especially on a heel, can cause infection, amputation, and even death.

Slough is often the term used by novice health care professionals to describe anything other than granulation tissue or eschar. Slough is moist, soft, solid, or stringy dead tissue primarily composed of leukocytes, macrophages, fibroblasts, and other apoptotic cells. In addition to apoptotic cells, it also commonly contains bacteria and biofilms.

Stop sign Prolonged presence of nonviable tissue in the wound bed inhibits the normal healing trajectory by maintaining an inflammatory state. Inability to accurately identify anatomy and structures results in inappropriate debridement and risk of harm to the patient. When planning treatment, it is important to remember different tissue types can appear similar; however, the underlying etiology may be unrelated and therefore require a completely different method of care (Young, 2015). Before debriding, stop and think.