What Causes Bed Sores?

Bed sores, also called pressure ulcers or pressure injuries, happen when constant pressure cuts off blood flow to an area of skin. That pressure usually comes from lying in one position too long or sitting without shifting your weight. When blood can’t reach the tissue, the skin and the tissue underneath begin to break down and die.

What Causes Bed Sores?

The direct cause of a bed sore is unrelieved pressure on a specific area of the body. This pressure squeezes small blood vessels closed. Without fresh blood delivering oxygen and nutrients, cells start to die. The damage begins in the deepest tissue layers and works its way up to the skin surface, which is why a sore can look small on the outside but be much larger underneath.

Pressure alone is not the only factor. Friction and shear also play a major role. Friction happens when skin rubs against sheets or clothing. Shear happens when the skin stays in place but the tissue underneath shifts — this commonly occurs when a bed is raised at the head and the body slides down. Both actions stretch and tear small blood vessels, making the skin far more vulnerable to damage.

Who Is Most at Risk for Developing Bed Sores?

Anyone who cannot move independently for long periods is at risk. People confined to a bed or a wheelchair for days, weeks, or months face the highest danger. Limited mobility is the single strongest risk factor because it prevents the natural, unconscious position changes that healthy people make dozens of times each night.

Several other conditions increase risk significantly. Poor nutrition and dehydration weaken the skin and reduce its ability to repair itself. Loss of sensation — from spinal cord injury, stroke, or nerve damage — means a person cannot feel the discomfort that normally triggers a position change. Advanced age also raises risk because aging skin is thinner, less elastic, and heals more slowly. Incontinence adds moisture that softens the skin and makes it far more prone to breakdown.

Which Parts of the Body Are Most Affected?

Bed sores develop over bony areas where the skin is thin and there is little fat or muscle to cushion the pressure. In people who lie on their back, the most common sites are the tailbone, heels, shoulder blades, elbows, and the back of the head. For people who lie on their side, the hips, ankles, and ears are most vulnerable. People who sit in wheelchairs most often develop sores on the tailbone and the shoulder blades.

The location matters because it tells caregivers which positions carry the highest risk. The heels are particularly problematic because the entire weight of the leg focuses on a very small area. The tailbone is also high-risk because it bears weight in both lying and sitting positions.

What Are the Stages of Bed Sores?

Medical professionals classify bed sores into four stages based on how deep the damage goes. This staging system guides treatment and helps track whether a sore is healing or getting worse.

• Stage 1: The skin is intact but red and does not turn white when pressed. On darker skin, the area may look purple, blue, or darker than the surrounding skin. The area may feel warm, firm, or painful.
• Stage 2: The skin has broken open or formed a shallow ulcer. The wound may look like a blister, either intact or ruptured. Some tissue loss is visible, but the wound is still shallow.
• Stage 3: The sore is now a deep crater. Damage extends through the skin layers into the fat tissue beneath. The wound may show yellowish dead tissue called slough.
• Stage 4: The deepest stage. The sore extends into muscle, bone, or supporting structures like tendons and ligaments. Extensive tissue death is common at this stage.

Two additional categories exist. One is called “unstageable” when the wound is covered by dead tissue, making it impossible to see how deep it goes. The other is a deep tissue injury where the skin looks purple or maroon but has not broken open yet — this indicates serious damage below the surface.

How Can Bed Sores Be Prevented?

Prevention centers on one principle: relieve the pressure before tissue damage occurs. The most effective method is regular repositioning. People who are bedbound should be turned at least every two hours. People in wheelchairs should shift their weight every 15 to 30 minutes. These intervals are standard clinical guidance and are well supported by evidence.

Support surfaces make a significant difference. Specialized mattresses, mattress overlays, and wheelchair cushions redistribute pressure away from vulnerable bony areas. These products range from simple foam overlays to advanced alternating-pressure air mattresses that cycle pressure across the body. A person at high risk should use one of these surfaces consistently.

Skin care is equally important. The skin should be kept clean and dry, especially in areas affected by moisture. Daily skin inspections are critical — checking every bony area for redness or color changes allows early detection before a sore progresses past Stage 1. For people with limited mobility, caregivers must perform these checks. Pay particular attention to heels, which should be protected with pillows or heel offloading devices so they float completely free of the mattress.

Nutrition cannot be overlooked. Adequate protein, calories, and hydration are necessary for skin integrity and wound healing. A person who is malnourished cannot maintain healthy skin, and once a sore develops, poor nutrition severely impairs recovery.

How Are Bed Sores Treated?

Treatment depends entirely on the stage of the sore. The first step in every case is removing pressure from the affected area. A wound cannot heal while it is being compressed. This may require stricter repositioning schedules, a different support surface, or both.

Stage 1 sores often resolve within days once pressure is relieved. Stage 2 sores require keeping the wound clean and covered with an appropriate dressing that maintains a moist healing environment. Stage 3 and Stage 4 sores need professional medical care. Treatment may involve surgical removal of dead tissue, called debridement, specialized wound dressings, and possibly antibiotics if infection is present. Severe cases can require surgery to close the wound or remove damaged bone.

Infection is the most serious complication. An infected bed sore can spread to deeper tissues, bones, or the bloodstream, leading to sepsis — a life-threatening condition. Warning signs include increased redness, warmth, swelling, pus, foul odor, or fever. Any of these symptoms require immediate medical attention.

Can Bed Sores Be Reversed?

Yes, but the outlook depends on the stage at which treatment begins. Stage 1 and Stage 2 sores generally heal well with consistent pressure relief and proper wound care. Stage 3 and Stage 4 sores are much harder to treat and may take months to heal. Some deep sores never fully close and require long-term management rather than complete healing.

Healing is a slow process. Even with perfect care, a deep sore can take weeks or months to rebuild tissue. The risk of recurrence is high — once a person has had a bed sore, that area of skin remains more fragile and vulnerable to future breakdown.