What Are Pressure Sores? Causes, Stages, and Treatment

Pressure sores, now more commonly called pressure injuries, are areas of localized damage to the skin and underlying tissue caused by sustained mechanical loading, usually over a bony prominence or under a medical device. The core problem is straightforward: when tissue is compressed for long enough, blood flow is cut off and cells begin to die. What makes pressure injuries deceptively dangerous is that the worst damage often starts deep, near the bone, and may not be visible on the skin surface until it has become severe. In the United States alone, the annual cost of hospital-acquired pressure injuries may exceed $26.8 billion, and the consequences for patients range from chronic pain to life-threatening bloodstream infections.

How Pressure Injuries Form

The fundamental cause is pressure ischemia, the choking off of blood supply to tissue caught between a hard surface (like a mattress or wheelchair seat) and a bony prominence underneath the skin.¹ But the picture is more nuanced than simple pressure alone. When soft tissue is deformed, cells start dying on a microscopic level within minutes, though it can take hours of sustained loading before the damage becomes clinically visible.² Two distinct patterns emerge depending on the depth of injury. Superficial skin damage is primarily driven by shear, the sideways sliding force that occurs when the body shifts against a surface. Deeper injuries tend to result from high pressures combined with shear directly over bony prominences.²

Moisture adds another layer of risk. When skin is wet from sweat, urine, or wound drainage, the friction between skin and the support surface increases. Repositioning a patient whose skin is damp creates higher shear stresses and can itself trigger skin breakdown.³ This is one reason incontinence is such a potent risk factor: the skin stays persistently moist, and every turn in bed becomes an opportunity for friction-related damage.

Where Pressure Injuries Develop

The most common sites are the sacrum (the flat bone at the base of the spine), the ischium (the “sit bones”), the trochanters (bony protrusions at the outer hips), and around the ankles and heels.⁴ The pattern depends on position. A person lying on their back is most vulnerable at the sacrum and heels. Someone lying on their side loads the trochanter. Wheelchair users load the ischium. Deep tissue pressure injuries most often appear over the coccyx or sacrum, buttocks, and heels.⁵

Medical devices create an entirely separate category. Any device in direct contact with the skin, from oxygen tubing and cervical collars to casts and splints, can cause a pressure injury that mirrors the shape of the device.⁶ These injuries are easy to overlook because clinicians may not think to check under a device that is doing its therapeutic job.

The Staging System

Pressure injuries are classified by how deep the damage goes. The revised staging system from the National Pressure Injury Advisory Panel uses Arabic numerals and the word “injury” rather than the older “ulcer” terminology. The revised definition recognizes that injuries typically occur over bony prominences or under medical devices.⁷

Stage 1: Intact skin with a localized area of nonblanchable redness. When you press on normal reddened skin, it briefly turns white (blanches) and then returns to red. In a Stage 1 injury, the redness does not blanch. The area may feel warmer, cooler, firmer, or softer than surrounding skin.
Stage 2: Partial-thickness loss of skin, exposing the dermis. This may look like a shallow open sore, a blister, or a shiny or dry wound bed. The revised definition for Stage 2 specifically seeks to clarify the difference between moisture-associated skin damage and injury caused by pressure or shear.
Stage 3: Full-thickness skin loss. Fat may be visible in the wound, and there may be undermining or tunneling, but bone, tendon, and muscle are not exposed.
Stage 4: Full-thickness skin and tissue loss with exposed or directly palpable bone, tendon, fascia, muscle, or cartilage. These wounds often involve extensive undermining and tunneling.
Unstageable: Full-thickness injury obscured by dead tissue (slough or eschar). The true depth cannot be determined until the wound is cleaned.
Deep tissue pressure injury: A distinct and dangerous pattern where damage begins in the muscle closest to the bone and may not be visible early on. Its hallmark is rapid deterioration despite appropriate preventive care.

Why Deep Tissue Injuries Are So Tricky

Deep tissue pressure injuries deserve special attention because they defy intuition. The skin surface may show only a purple or maroon discoloration, or a blood-filled blister, while underneath the tissue is already severely damaged. In patients with lighter skin tones, the classic presentation is a distinct area of purple or maroon discoloration with a defined border and surrounding redness.⁸ The diagnosis is harder in patients with darker skin tones, where persistent redness and hyperpigmentation rather than blanching response should be used to identify the injury.⁸ This disparity in visibility means pressure injuries in darker-skinned patients are frequently detected later, when the damage is more advanced.

The diagnostic process begins with accounting for any periods when the patient was immobile and under sustained pressure, such as time spent lying on the ground before being found, or time flat during surgery.⁸ Many other skin conditions can mimic a deep tissue injury, including bruising from falls, skin tears, and certain vascular conditions, so thorough history-taking matters.

Who Is Most at Risk

Anyone who cannot move independently or who cannot feel pain normally is at elevated risk. That includes people with spinal cord injuries, those under heavy sedation or anesthesia, stroke patients, and individuals with advanced dementia who may not shift their weight. Among people with spinal cord injuries, the global prevalence of pressure injuries is roughly a third, based on a meta-analysis of 24 studies involving about 600,000 participants.⁹ The highest rates were observed in Africa, at about 41%.⁹

In hospitals, structured risk assessment tools help identify vulnerable patients early. The most widely used is the Braden Scale, which scores patients on sensory perception, moisture exposure, activity level, mobility, nutrition, and friction/shear. A large meta-analysis of 60 studies found the Braden Scale has moderate accuracy for predicting pressure injury risk, with a pooled sensitivity of about 78% and specificity around 72%.¹⁰ In intensive care patients, a modified version that incorporates albumin levels performed somewhat better than the standard Braden Scale.¹¹ No single tool is perfect, though. The reality is that clinical judgment still plays a large role, and these scores are meant to supplement rather than replace a nurse’s observations.

Prevention Through Repositioning and Support Surfaces

Turning and repositioning patients to redistribute pressure is the backbone of prevention, but the evidence behind specific schedules is thinner than you might expect. A Cochrane review pooling data from three trials with over a thousand participants found no clear difference between repositioning every two hours versus every four hours.¹² The proportion of patients developing pressure injuries was lower in the groups turned more frequently, but the differences did not reach statistical significance and could have been due to chance. The review also found no clear difference between a 30-degree tilt and a 90-degree lateral position. A separate systematic review reached the same conclusion: the optimal repositioning frequency remains unclear.¹³

This does not mean repositioning is useless. It means we lack enough high-quality studies to pin down the exact schedule. The general principle that relieving pressure reduces tissue damage is well supported by the underlying biology. What the evidence tells us is that rigid “every two hours” protocols may not be the magic number they are often treated as, and the ideal frequency probably depends on the patient’s individual risk profile and the quality of the mattress they are on.

Support surfaces, from specialty foam mattresses to alternating-pressure air mattresses, are the other major preventive tool. A Cochrane overview and network meta-analysis found that several types may reduce pressure injury risk compared with standard hospital foam mattresses. Static air overlays cut the risk roughly in half, and alternating-pressure air mattresses reduced risk by about a third, though the evidence was rated low-certainty.¹⁴ A large randomized trial of over 2,000 patients comparing alternating-pressure mattresses with high-specification foam mattresses found that the alternating-pressure group had somewhat fewer pressure injuries and lower total healthcare costs, largely because they spent less time in the hospital.¹⁵

Treatment Once a Pressure Injury Develops

Treatment depends heavily on the stage. Early-stage injuries (Stages 1 and 2) are primarily managed by removing the source of pressure, keeping the wound clean, and managing moisture. For more advanced injuries, the toolkit expands.

Wound dressings are a mainstay, but the evidence for any one dressing type over another is surprisingly weak. A Cochrane review of hydrocolloid dressings for pressure ulcers found very low-certainty evidence. One small trial suggested hydrocolloid dressings might be better than gauze for complete healing, but other trials showed no clear difference between hydrocolloid and basic wound-contact dressings or foam dressings.¹⁶ In practice, clinicians choose dressings based on wound characteristics like the amount of drainage, presence of dead tissue, and infection status, adjusting as the wound evolves.

For larger or more complex wounds, negative pressure wound therapy (sometimes called wound vacuum therapy) is increasingly used. The device applies controlled suction through a sponge placed in the wound, sealed with an airtight film dressing. This promotes healing through several mechanisms: it draws the wound edges closer together, drains inflammatory fluids, stabilizes the wound environment, and creates microscopic tissue deformations that stimulate cell growth.¹⁷ Additional proposed mechanisms include increased blood flow and the promotion of new blood vessel formation, though earlier claims about bacterial clearance have not been confirmed in basic research.¹⁸

Stage 4 injuries that reach bone, tendon, or muscle may require surgical intervention, including debridement (removal of dead tissue) and reconstructive procedures using tissue flaps.

Nutrition and Healing

What a patient eats turns out to matter considerably for pressure injury healing, and undernutrition is both a risk factor for developing them and a barrier to recovery. Increased needs for energy, protein, zinc, and vitamins A, C, and E have been documented, along with amino acids like arginine and glutamine, though the ideal intake amounts remain unclear.¹⁹

A study in malnourished nursing home patients found that those receiving a higher-protein diet (about 24% of calories from protein) had a significant decrease in pressure ulcer surface area, while those on a standard 14%-protein diet did not. The effect was especially pronounced in the most severe (Stage 4) injuries.²⁰ A Cochrane review found that protein and micronutrient supplements may slightly improve healing rates compared with standard diet. In three studies involving 577 participants, about 37% of supplemented patients achieved complete healing versus 25% on standard diet. Supplements containing arginine did not clearly increase complete healing, but they were associated with a modest reduction in wound area.²¹

Complications That Make Pressure Injuries Deadly

Pressure injuries are not just painful wounds. They can become gateways for serious, sometimes fatal infections. The main infectious complications include cellulitis, abscess formation, osteomyelitis (bone infection beneath the wound), and bacteremia (bacteria in the bloodstream). In a prospective study of patients who developed bacteremia from pressure ulcers, osteomyelitis was present in about 23% of cases, and overall mortality was 41%.²² The risk factors most strongly associated with dying were hospital-acquired bacteremia, infections involving multiple bacterial species, and severely low albumin levels, all pointing to the role of the patient’s overall debilitation.²²

The Toll on Quality of Life

The physical and emotional burden of living with a pressure injury is often underestimated. A systematic review of quality-of-life studies found that patients consistently report negative emotions including feelings of helplessness, frustration, anxiety, and diminished dignity.²³ Pain is a constant feature, described as continuous, difficult to control, and not necessarily proportional to the stage of the wound. The pain can be inflammatory or neuropathic, and the review noted that medical and nursing staff frequently underperceive and undermeasure it.²³ Social activity also suffers: the combination of required bed rest, wound symptoms like drainage and odor, and ongoing treatment demands leaves many patients isolated.

Pressure Injuries in Children and Newborns

Pressure injuries in children are a distinct problem from their adult counterpart, not a scaled-down version of it. In neonates, the body regions where injuries develop are different because the proportions of the body are different. A young child’s head is proportionally larger and heavier, with less fat padding the skull, making the back of the head (occiput) a frequently reported site for pressure injury in infants through about age five.²⁴ In neonates specifically, the most common locations are the occiput, sacrum, ears, heels, ankles, and nose.²⁵

The biggest risk factor for neonates is medical devices. The incidence of device-related pressure injury in newborns ranges from 50% to 90% of all neonatal pressure injuries.²⁵ Endotracheal tubes, noninvasive ventilation masks, pulse oximetry probes, and other monitoring equipment create sustained pressure on fragile, immature skin. Additional risk factors include low birth weight, prematurity, low blood pressure, low oxygen levels, and prolonged stays in the neonatal intensive care unit.²⁵ Children younger than five also cannot properly distinguish pressure sensations from other feelings, so they do not instinctively shift to relieve discomfort the way an older child or adult would.²⁴

The Economic Weight

Hospital-acquired pressure injuries are among the costliest complications to treat. In the United States, the total annual cost may exceed $26.8 billion, with roughly 59% of those costs driven by a relatively small proportion of Stage 3 and Stage 4 full-thickness wounds, which consume disproportionate amounts of clinician time and hospital resources.²⁶ Many healthcare systems now treat hospital-acquired pressure injuries as a quality metric and, in some payment models, hospitals are not reimbursed for the added costs of treating them. This creates a strong financial incentive for prevention, which is substantially cheaper than managing a wound that has progressed to an advanced stage.

Emerging Detection Technologies

One of the persistent challenges with pressure injuries is that by the time they become visible on the skin surface, the underlying damage may already be extensive. Researchers have been exploring technologies to catch injuries earlier. Sub-epidermal moisture (SEM) scanning is a point-of-care technology that measures localized swelling in tissue beneath the skin’s surface, which can be an early sign of damage before any visible change appears.²⁷ Studies have found that SEM values increase in step with increasing tissue damage, with the sacrum and heels being the most common sites where early changes are detected.²⁸

Other approaches, including skin temperature monitoring and surface hydration measurement, have been investigated but so far appear less reliable. A prospective study comparing SEM to temperature, skin hydration, and pain assessments found no consistent correlation between these other measures and early pressure injury development, suggesting they are not dependable standalone screening tools.²⁹ The field is still young, and none of these technologies has yet replaced visual skin assessment as the standard of care. But SEM scanning in particular is generating interest as a potential way to identify at-risk tissue in patients whose skin tone makes visual inspection less reliable, a gap that has long been recognized as a source of health disparities in pressure injury detection.

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