Pressure Ulcer Classification

Pressure ulcers/injuries are classified into 6 stages according to the amount of affected tissue.

Why Is Correct Diagnosis And Classification Important?

Not all wounds are the same, even though they may look similar on the surface. Correctly identifying a pressure ulcer is the first and most important step in choosing the right treatment. Pressure ulcers can easily be mistaken for wounds caused by other conditions, which can lead to incorrect care and delayed healing. Having one clear way to describe pressure ulcers helps everyone understand how serious the wound is and allows healthcare professionals to talk about it more easily.

How Are Pressure Ulcers Classified?

EPUAP/NPIAP/PPIAP uses classification where pressure ulcers are classified based on how much tissue is affected and/or lost.
The classification is mainly based on what can be seen and felt (to some extent) in the wound and surrounding skin. Healthcare providers look at the type of tissue present, and may also feel for temperature differences or changes in firmness. However, it’s important to note that the full extent of tissue damage is not always visible, especially in deeper wounds.

EPUAP Classification

EPUAP/NPIAP/PPIAP Classification recognizes 6 different types of pressure ulcers¹:

Category/Stage I Pressure Ulcer: Non-blanchable erythema – The skin is intact but shows redness (or a change in colour in darker skin). The area may feel painful, warmer, cooler, softer, or firmer than nearby skin. This is the first sign of risk.
Category/Stage II Pressure Ulcer: Partial thickness skin loss – The top layer of skin is damaged, appearing as a shallow open sore or a blister. The wound bed looks red or pink but there is no dead tissue (slough).
Category/Stage III Pressure Ulcer: Full thickness skin loss – The ulcer extends through the skin into the fat underneath. It may look deep, depending on the body area. Dead tissue (slough) may be present, and the wound can have tunneling or undermining. Bone, tendon, or muscle are not visible.
Category/Stage IV Pressure Ulcer: Full thickness tissue loss – The ulcer extends through skin and fat, exposing bone, tendon, or muscle. Dead tissue may be present, and tunneling is common. These ulcers can cause serious complications like bone infection.
Unstageable Pressure Ulcer (covered in eschar or slough) – The wound is covered with dead tissue (slough or eschar), making it impossible to see how deep it is. Until this covering is removed, the stage cannot be determined. On the heel, intact dry eschar may serve as the body’s natural protection and should not be removed.
Suspected Deep Tissue Injury: Depth unknown – The skin may look purple, maroon, or like a blood-filled blister. This signals damage beneath the surface, which can quickly progress to a more severe ulcer, even if treated. It can be harder to detect in darker skin tones.

Pressure ulcers can also develop on the moist inner linings of the body (mouth, nose, digestive or urinary tracts) where tubes or catheters are used. These are known as mucosal membrane pressure ulcers². Because the tissues here are very different from skin, they cannot be classified with the same systems used for regular pressure ulcers.

Why Depth Can Be Misleading?

It might seem logical to classify a pressure ulcer based on how deep it is, but this can be misleading. The depth of a pressure ulcer depends on the location on the body, and how much fat or tissue is underneath the skin. For example¹:

In areas with very little tissue – like the bridge of the nose, the back of the head, behind the ears, or the ankles – even a shallow-looking ulcer can be classified as Stage IV, the most severe stage, because it may expose muscle, tendon, or bone.
In contrast, in areas with more fat and tissue, like the buttocks, an ulcer may appear deep but may not reach the muscle or bone. In that case, it would be classified as a Stage III ulcer.

Classifying Pressure Ulcers In Darker Skin Tones

In people with darker skin, early signs of pressure ulcers can be harder to see. Redness (erythema) and infections like cellulitis may be missed, especially in the first stage of injury. To improve detection, healthcare providers should check for other changes, such as:

Warmer skin in the affected area
Swelling or fluid under the skin (sub-epidermal moisture)
Hardness or change in skin texture compared to nearby areas
Localized pain

Special tools, like skin temperature checks, moisture measurement devices, and skin tone color charts, can help identify pressure ulcers more accurately. Pain assessment is also an important part of the evaluation process.¹

Summary

Understanding how pressure ulcers are classified helps ensure that people receive the right care at the right time. While visual inspection is key, it’s important to remember that looks can be deceiving, and expert assessment is essential for accurate diagnosis and treatment planning.

If you or someone you care for is at risk of pressure ulcers, talk to a healthcare provider about prevention, early signs, and how classification guides care decisions.

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References

European Pressure Ulcer Advisory Panel, National Pressure Injury Advisory Panel and Pan Pacific Pressure Injury Alliance. Prevention and Treatment of Pressure Ulcers/Injuries: Clinical Practice Guideline. The International Guideline. Emily Haesler (Ed.). EPUAP/NPIAP/PPPIA: 2019.
Coyer FM, Stotts NA, Blackman VS. A prospective window into medical device-related pressure ulcers in intensive care. Int Wound J, 2014; 11(6): 656-64.