A diabetic ulcer is not a pressure ulcer. They are two distinct wound types with different causes, different locations on the body, and different treatment approaches. However, the confusion is understandable because pressure plays a role in both, and people with diabetes are at higher risk for developing pressure ulcers too. The medical system codes them separately, and getting the distinction right matters for proper treatment.
What Causes Each Type of Ulcer
A diabetic foot ulcer develops primarily because of nerve damage (neuropathy) and poor blood flow, both consequences of prolonged high blood sugar. Over time, diabetes stiffens ligaments, weakens the coordination of foot muscles, and dulls sensation. When you can’t feel pain in your feet, you don’t notice a blister from a tight shoe, a sharp object underfoot, or excessive pressure on a specific spot. Meanwhile, reduced blood flow means even minor injuries heal slowly or not at all. The combination of not feeling damage and not being able to repair it is what makes diabetic ulcers so common and so persistent.
Pressure ulcers, by contrast, are caused by sustained external compression of soft tissue between a bony prominence and an outside surface, like a mattress or wheelchair. When tissue is squeezed for too long, the tiny blood vessels inside it collapse. Pressures exceeding normal capillary range cut off oxygen delivery, and if that compression isn’t relieved, a pressure injury can begin forming in as little as three to four hours. Shearing forces, like those created when a patient slides down an inclined bed, add to the damage by pulling deeper tissues in one direction while the skin stays put. Pressure ulcers are fundamentally a problem of immobility.
Where They Appear on the Body
Location is one of the clearest ways to tell them apart. Diabetic foot ulcers generally show up on the sole of the foot, the tops of the toe joints, and the tips of the toes. These are areas that bear weight during walking, where mechanical stress concentrates on spots the person can no longer feel. Calluses often form first, increasing pressure further until the skin breaks down underneath.
Pressure ulcers form over bony prominences where the body presses against a surface during prolonged sitting or lying down. The sacrum (lower back), heels, hips, and shoulder blades are classic sites. On the foot specifically, pressure ulcers tend to appear on the heel or the outer bony edge of the foot, caused by contact with beds, footrests, or wheelchair components. A wound on the bottom of the foot in someone who walks is far more likely to be a diabetic ulcer. A wound on the heel of someone who has been bedridden points toward a pressure injury.
The Confusing Overlap
Here’s where it gets tricky: pressure is a factor in roughly 90% of diabetic ulcers on the sole of the foot. That pressure comes from foot deformities, poorly fitting shoes, or built-up calluses rather than from being immobile in a bed or chair. It’s internal, repetitive mechanical stress during walking, not sustained external compression from lying still. The source and nature of the pressure differ even though the word “pressure” applies to both.
Diabetes also genuinely increases the risk of developing true pressure ulcers. The nerve damage that causes diabetic foot ulcers also makes a person less likely to feel discomfort from prolonged compression elsewhere on the body, so they don’t shift position as often. Poor circulation from diabetes reduces oxygen delivery to compressed tissues, making them more vulnerable to breakdown and slower to heal once injured. A person with diabetes who is hospitalized or uses a wheelchair can absolutely develop a pressure ulcer on their heel, and that wound would be classified differently from a diabetic foot ulcer on their sole, even though diabetes contributed to both.
How They’re Classified and Graded
The two wound types use entirely separate grading systems. Pressure ulcers are staged from Stage 1 (intact skin with non-blanchable redness) through Stage 4 (full-thickness tissue loss exposing bone, tendon, or muscle). This staging system focuses on depth of tissue destruction.
Diabetic foot ulcers use the Wagner classification, which tracks both depth and the presence of infection or tissue death:
- Grade 0: Skin intact but foot deformities create risk
- Grade 1: Superficial ulcer
- Grade 2: Deeper wound extending through the full skin thickness
- Grade 3: Deep abscess or bone infection
- Grade 4: Partial gangrene of the forefoot
- Grade 5: Extensive gangrene
In medical coding, these wounds fall under completely different categories. Pressure ulcers are coded under L89, which captures the site, stage, and which side of the body is affected. Diabetic ulcers are coded as non-pressure ulcers under L97 or L98, paired with a diabetes code that identifies the type and complication. A diabetic heel ulcer, for example, would be coded with both a diabetes code and a non-pressure chronic ulcer code, not as a pressure injury.
Why the Distinction Matters for Treatment
Getting the diagnosis right determines what treatment you receive, and the approaches are meaningfully different.
For diabetic foot ulcers, the cornerstone of treatment is offloading, which means redistributing weight away from the wound. Total contact casts and other non-removable devices are the most effective options because they ensure the pressure reduction actually happens consistently. Standard therapeutic shoes alone don’t reliably heal active ulcers. With proper offloading, an uncomplicated plantar ulcer typically heals in six to eight weeks. But offloading alone isn’t enough if blood flow is severely impaired, infection is present, or bone deformities keep creating abnormal pressure points. Those underlying problems need to be addressed simultaneously.
For pressure ulcers, the primary intervention is relieving the sustained external compression. This means regular repositioning (turning schedules for bedridden patients), specialized pressure-redistributing mattresses or cushions, and keeping skin dry and protected from friction. The goal is eliminating the mechanical cause, which is immobility against a surface, rather than modifying how someone walks.
Both wound types require attention to nutrition, infection control, and circulation. But a diabetic foot ulcer treated only with repositioning schedules would continue to worsen every time the person walked, and a pressure ulcer treated only with offloading footwear would keep deteriorating if the patient remained immobile against a bed surface. The wrong diagnosis leads to the wrong intervention targeting the wrong mechanical problem.
How to Tell Them Apart on the Foot
The foot is the one area where these two wound types can genuinely be hard to distinguish, especially in someone with diabetes who is also immobile. A few practical markers help clarify which you’re dealing with. Wounds on the sole of the foot, particularly under the ball of the foot or the big toe, with surrounding callus buildup, are characteristic of diabetic neuropathic ulcers caused by walking. Wounds on the back or sides of the heel, particularly in someone who spends significant time in bed or a wheelchair, are more consistent with pressure injuries caused by contact with external surfaces.
The patient’s mobility level is often the deciding factor. An ambulatory person with diabetes and neuropathy who develops a wound on the bottom of their foot almost certainly has a diabetic ulcer. A bedridden person with diabetes who develops a heel wound likely has a pressure ulcer, though their diabetes is making it harder to heal. In some cases, both mechanisms contribute, and the wound reflects elements of each. Accurate documentation of the wound’s location, the patient’s activity level, and the underlying conditions guides the correct classification.