Sores on the legs most commonly develop from problems with blood circulation, either in the veins or arteries. Venous disease alone accounts for roughly 1.1% of all adults over 18, and it’s the single largest cause of chronic leg ulcers. But circulation isn’t the only culprit. Diabetes, pressure on the skin, infections, and inflammatory conditions can all produce open wounds on the lower legs that refuse to heal.
Venous Insufficiency: The Most Common Cause
When the valves inside your leg veins stop working properly, blood pools in the lower legs instead of flowing back toward the heart. This creates sustained high pressure inside the veins, which pushes inflammatory cells and fluid into the surrounding tissue. Over time, the skin breaks down and an ulcer forms.
Venous ulcers have a recognizable look. They tend to be shallow with irregular edges, a moist base, and well-defined borders. You’ll usually find them on the inner ankle or the lower calf, particularly over bony areas. The surrounding skin often shows other signs of long-standing vein problems: swelling, varicose veins, reddish-brown discoloration, or a hardened, tight texture in the skin (sometimes described as an “inverted champagne bottle” shape where the calf narrows while the ankle stays swollen). White, scarred patches of skin near the ankle are another telltale sign.
With proper compression therapy, venous leg ulcers often heal within six months. Without treatment, they can persist for years and frequently recur.
Poor Arterial Blood Flow
Arterial ulcers form for the opposite reason: not enough blood is reaching the legs. Plaque buildup inside the arteries (peripheral artery disease) is the most common cause, but diabetes, inflammatory conditions affecting blood vessels, and radiation side effects can also restrict arterial flow. When oxygen and nutrient delivery drops below what the tissue needs to survive, the skin dies and an open sore develops.
These sores typically appear on pressure points: toes, heels, ankles, and bony prominences of the foot. They look different from venous ulcers. Arterial ulcers tend to have a “punched out” appearance with sharp edges, a pale or gray wound base, and little drainage. The surrounding skin often feels cool to the touch, and you may notice that foot pulses are weak or absent. Arterial ulcers are generally more painful than venous ulcers, especially at night or when the legs are elevated.
Diabetic Foot and Leg Ulcers
Diabetes creates a perfect storm for leg and foot sores. About 63% of diabetic foot ulcers trace back to a combination of three factors: nerve damage, repetitive pressure or trauma, and foot deformities. When diabetes damages the nerves in your feet (peripheral neuropathy), you lose the ability to feel pain from blisters, cuts, or pressure points. A pebble in your shoe or a poorly fitting shoe can cause tissue damage you never notice.
Diabetes also damages arteries, particularly the smaller vessels below the knee. A classic finding is having a pulse behind the knee but no detectable pulse at the foot. This means wounds that do form get starved of the blood supply they need to heal. Add in the fact that high blood sugar impairs the immune system, and small injuries can rapidly progress into deep, infected ulcers. Restoring blood flow is critical for healing, regardless of what wound care is applied on the surface.
Pressure Injuries
Pressure sores develop when sustained force on the skin cuts off blood flow to the tissue underneath. On the legs, the ankles and heels are the most vulnerable spots because bone sits close to the skin surface with little cushioning. People who are bedridden, use a wheelchair, are paralyzed, or have limited mobility are at highest risk.
The earliest stage looks like a patch of reddened skin (or a darker area on deeper skin tones) that doesn’t fade when you press on it. There’s no open wound yet, but the tissue is already damaged. Without pressure relief, the area progresses to a blister or shallow open sore, then deepens into muscle and potentially down to bone. Moisture from sweat, urine, or stool accelerates the process, as does sliding or being dragged across bedsheets.
Inflammatory and Autoimmune Causes
Not all leg sores come from circulation problems or pressure. Some are driven by the immune system attacking the skin or blood vessels directly.
Pyoderma Gangrenosum
This condition starts as a small bump or pimple-like spot that rapidly breaks down into a painful ulcer. The hallmark feature is a raised, violet-colored border around the wound, with a base that looks raw and produces pus. Pyoderma gangrenosum is often associated with inflammatory bowel disease, arthritis, or blood disorders, though it can appear on its own. There’s no single test that confirms it. Diagnosis relies on the characteristic appearance and ruling out other causes.
Vasculitis
When the immune system attacks small blood vessels in the skin, it causes inflammation that damages vessel walls and lets red blood cells leak into the surrounding tissue. The result is palpable purpura: raised, reddish-purple spots that you can feel with your fingernail. These spots most commonly cluster on the lower legs and can progress to shallow ulcers. Vasculitis can be triggered by infections, medications, or autoimmune diseases, or it can occur without an identifiable cause.
How Doctors Tell These Apart
Because the treatment for each type of leg sore is so different, getting the right diagnosis matters. One of the first tests is an ankle-brachial pressure index (ABPI), which compares blood pressure readings at the ankle to those in the arm. This quick, noninvasive check reveals whether arterial disease is contributing to the problem. If arterial disease is suspected, imaging such as duplex ultrasound, CT angiography, or MR angiography provides a detailed look at blood flow.
Beyond blood flow testing, doctors assess the wound’s location, depth, shape, and the condition of surrounding skin. A wound on the inner ankle with swelling and skin changes points toward venous disease. A painful wound on the toes with cool, pale skin suggests arterial insufficiency. Lab work, skin biopsies, and blood sugar testing help identify inflammatory, autoimmune, or diabetic causes.
Signs a Leg Sore Is Infected
Any open wound on the leg can become infected, and lower-leg sores are particularly vulnerable because of their distance from the heart and often compromised blood supply. Watch for increasing redness that spreads beyond the wound edges, warmth around the sore, swelling, worsening pain, fever, or chills. Blisters forming near the wound, skin dimpling (an orange-peel texture), or red streaking up the leg can signal cellulitis, a bacterial skin infection that can spread quickly and requires prompt treatment.