At a Glance: The difference between a stage 3 and a stage 4 pressure ulcer comes down to depth. A stage 3 pressure ulcer is a full-thickness wound where fat is visible, but muscle, tendon, and bone are not exposed. A stage 4 pressure ulcer is deeper, with muscle, tendon, ligament, or bone exposed. Both are serious wounds that need professional care, and both of their healing plans require taking pressure off the area with the right support surface.
A pressure ulcer, also called a pressure injury or bedsore, is damage to the skin and the soft tissue underneath it caused by sustained pressure. Usually, they form over a bony prominence such as the tailbone, hips, or heels. These wounds are described in four stages based on how deep the damage goes, and stages 3 and 4 are the two most severe. Knowing the difference helps patients and caregivers understand why a wound developed and what is necessary for recovery.
How Pressure Ulcers Are Staged
Pressure ulcers are staged by the depth of tissue damage. The staging system, which is used across the United States, runs from stage 1, the mildest, to stage 4, the most severe. The first two stages describe damage closer to the skin’s surface:
- Stage 1: Intact skin with an area of redness that does not turn white when pressed.
- Stage 2: Partial-thickness loss of skin, appearing as a shallow open wound or a blister.
Stages 3 and 4 are both full-thickness wounds, meaning the damage goes all the way through the skin. The difference between them is how far below the skin the damage reaches.
What Is a Stage 3 Pressure Ulcer?
A stage 3 pressure ulcer is a full-thickness wound where the skin integrity is lost entirely, and the fat layer beneath becomes visible. The wound often looks like a deep crater. Some features are common at this stage:
- Visible Fat: The yellowish fat tissue can be seen in the wound bed.
- Rolled Edges: The edges of the wound may thicken and roll under, a sign called epibole.
- Slough: A soft yellow or tan tissue may be present, though it does not hide the depth of the wound.
- Tunneling: The wound may extend under the skin at the edges, creating channels.
The defining feature of a stage 3 pressure ulcer is what is not exposed. Fascia, muscle, tendon, ligament, and bone remain covered. The depth varies by the location on the body, because areas with more fat, such as the hips, can develop deeper wounds than areas with little fat.
What Is a Stage 4 Pressure Ulcer?
A stage 4 pressure ulcer is the most severe stage. It is a full-thickness wound in which the damage extends past the fat and soft tissue to expose deeper structures while hindering blood flow. The defining feature is that muscle, tendon, ligament, cartilage, or bone is visible within the wound bed. Common characteristics include:
- Exposed Structures: Muscle, tendon, or bone can be seen or touched in the wound bed.
- Slough or Eschar: Dead tissue may be present, though it does not fully hide the wound’s depth.
- Undermining and Tunneling: The wound often spreads beneath the surrounding skin.
Because a stage 4 wound reaches bone, it carries a higher risk of serious complications, including bone infection, known as osteomyelitis, and blood infection, or sepsis. These wounds require close medical management and often take months to heal.
The Key Differences
The line between a stage 3 and a stage 4 pressure ulcer is drawn by what the wound exposes.
- Stage 3: Full-thickness skin loss with visible fat, but no exposed muscle, tendon, or bone.
- Stage 4: Full-thickness loss with exposed or palpable muscle, tendon, ligament, cartilage, or bone.
A wound covered by dead tissue cannot be staged at all. When slough or eschar hides the wound bed, a clinician labels it an unstageable pressure injury until the dead tissue is removed and the true depth can be seen. These wounds often present as either stage 3 or stage 4 ulcers once the slough or eschar is removed.
Who Is at Risk for Advanced Pressure Ulcers
A pressure ulcer rarely reaches stage 3 or 4 overnight. These deeper tissue wounds usually develop when an earlier-stage injury goes unnoticed or when pressure on an area continues without relief. Several risk factors make advanced wounds more likely:
- Limited Mobility: A patient who cannot reposition themselves stays under constant pressure, the single greatest risk factor.
- Poor Nutritional Status: Undernourished skin has less protective tissue and heals slowly, which lets a wound deepen.
- Reduced Sensation: A patient who cannot feel discomfort may not shift away from a pressure point.
- Moisture and Incontinence: Damp skin breaks down faster and is more vulnerable to pressure.
How Each Stage Is Treated
Both stages need professional wound management, and treatment shares a common foundation. Dead tissue is removed so healthy tissue can grow, typically through debridement using surgical, enzymatic, autolytic, or mechanical methods depending on the wound. The site is kept clean and appropriately moist with the right dressings. Infection is watched for and treated.
The difference is intensity and duration. A stage 3 wound may heal over weeks to months with consistent care. A stage 4 wound, because it reaches muscle and bone, often takes much longer and may require surgical treatment, such as removing infected bone or reconstructive surgery to close the wound.
One factor applies to both stages. The pressure that caused the wound has to be removed. A wound cannot heal while the same pressure keeps cutting off its blood supply. This is where the support surface becomes part of the treatment.
Relieving Pressure to Support Healing
For a stage 3 or stage 4 pressure ulcer, taking pressure off the wound is one of the most important parts of care. A standard mattress does not provide the pressure relief these wounds need, and a patient with limited mobility cannot shift their own weight to relieve it. A therapeutic support surface does that work and helps patients take preventive measures to prevent ulcers.
The right support surfaces are a core part of both treatment and pressure ulcer prevention. Alongside the surface, the rest of the care plan includes repositioning on a schedule, daily skin assessment to catch any change early, moisture management, and good nutrition. Together, these protect the wound and the skin around it.
Support Wound Healing at Home with Ethos
The difference between a stage 3 and a stage 4 pressure ulcer is depth. A stage 3 wound exposes fat, and a stage 4 wound exposes muscle, tendon, or bone. Both are serious, both need professional care, and both heal faster when the pressure that caused them is taken off the wound.
Ethos Therapy Solutions works with patients, families, and care teams to support wound healing at home. The air fluidized therapy beds, mattress overlays and replacements, and other solutions available through Ethos are built to help patients with limited mobility relieve pressure and prevent advanced wounds. To find the right surface, contact the Ethos team or explore the full range of options.