About 70% of leg ulcers are caused by chronic venous insufficiency, a condition where damaged valves in the leg veins allow blood to pool instead of flowing back to the heart. The remaining cases stem from arterial disease, diabetes, or less common inflammatory conditions. Understanding the specific cause matters because each type requires a different treatment approach.
Venous Insufficiency: The Most Common Cause
Your leg veins rely on one-way valves and calf muscle contractions to push blood upward against gravity. When those valves weaken or fail, blood flows backward and pools in the lower legs. This creates sustained high pressure inside the veins, a condition called chronic venous insufficiency (CVI).
That persistent pressure forces proteins out of the blood vessels and into the surrounding tissue, where they form a fibrous barrier around the skin cells. This barrier blocks oxygen and nutrients from reaching the skin. Over time, the skin becomes fragile, inflamed, and increasingly vulnerable to breakdown. Even a minor bump or scratch can open a wound that refuses to heal, becoming a venous leg ulcer. These ulcers typically appear on the inner ankle or lower calf and tend to be shallow, irregularly shaped, and weepy.
Venous ulcers affect roughly 1% of the global population between ages 18 and 64. With modern treatment, average healing time is about 12 weeks, though older studies reported averages closer to 9 months. About 20% of ulcers in those earlier series were still unhealed at two years, which underscores how important early, proper care is.
Warning Signs Before an Ulcer Forms
Venous ulcers rarely appear out of nowhere. The skin gives several warning signals as vein pressure damages the tissue over months or years. One of the earliest signs is a brownish discoloration around the ankles and lower legs, caused by iron deposits leaking from stressed blood vessels into the skin. You might also notice swelling that worsens throughout the day and improves overnight.
A more advanced stage is lipodermatosclerosis, where the skin and underlying fat layer become inflamed, hardened, and tight. In its early phase, this can look like a red, tender patch that’s often mistaken for a skin infection. Many people are initially prescribed antibiotics for suspected cellulitis when the real problem is vein-related inflammation. As the condition progresses, the skin turns dark, thick, and woody. This chronic hardening stage is considered a direct precursor to ulceration because the ongoing inflammation and scarring make wound healing extremely difficult. If you notice any of these changes, they signal that the underlying vein problem needs attention before a full ulcer develops.
Arterial Disease and Poor Circulation
Arterial leg ulcers account for a smaller share of cases but are often more serious. They happen when fatty deposits (atherosclerosis) narrow the arteries supplying blood to the legs, starving the tissue of oxygen. Peripheral artery disease (PAD) is the usual culprit. When blood flow drops severely, a condition called critical limb ischemia develops, where even small injuries or pressure points can trigger tissue death and open sores that won’t heal.
Arterial ulcers look and feel different from venous ones. They tend to appear on the feet, toes, or outer ankle rather than the inner leg. The edges are often well-defined and “punched out,” and the wound bed may look pale or gray. These ulcers are typically very painful, especially at night or when the legs are elevated, because gravity is no longer helping push blood downward into the limbs.
Doctors distinguish arterial from venous ulcers partly by measuring something called the ankle-brachial index (ABI), which compares blood pressure at the ankle to blood pressure in the arm. A normal reading falls between 0.9 and 1.4. A reading below 0.9 indicates arterial narrowing, and anything below 0.5 signals critical ischemia where the risk of tissue loss is high. Values above 1.4 suggest the arteries have calcified and become rigid, which is common in people with diabetes.
How Diabetes Leads to Ulcers
Diabetes creates a perfect storm for leg and foot ulcers through two overlapping problems: nerve damage and blood vessel damage. Persistently high blood sugar injures the small nerves in the feet, a condition called sensory neuropathy. This strips away the ability to feel pain, pressure, vibration, and temperature. Without those protective signals, small wounds, blisters, or pressure sores go completely unnoticed. People walk on injuries for days or weeks, re-traumatizing the same spot until a full ulcer forms.
At the same time, high blood sugar damages the lining of blood vessels throughout the body. In the feet, this microvascular damage means that even when a wound does form, the body can’t deliver enough oxygen and nutrients to repair it. The numb foot compounds the problem further: normally, when tissue is injured, nerves trigger local blood vessels to dilate and increase blood flow to the area. In a foot without sensation, that reflex doesn’t fire, so the wound is starved of healing resources from the start. This is why both patients and clinicians sometimes underestimate the severity of diabetic ulcers. The wound may look manageable, but the combination of lost sensation and impaired circulation makes it far more dangerous than it appears.
Less Common Causes
While vascular disease and diabetes account for the majority of leg ulcers, several other conditions can cause them. Pyoderma gangrenosum is an inflammatory skin condition where sterile pustules or red bumps rapidly break down into deep, intensely painful ulcers with distinctive purple, undermined edges. Its exact cause is unclear, but it’s linked to autoimmune conditions like inflammatory bowel disease and rheumatoid arthritis. These ulcers can look infected but aren’t caused by bacteria, and treating them with antibiotics alone won’t help.
Vasculitis, where the immune system attacks blood vessel walls, can also produce leg ulcers by cutting off blood supply to patches of skin. Necrobiosis lipoidica, an inflammatory condition most common in people with diabetes, causes the skin to thin progressively until painful ulcers form. Other documented causes include scleroderma, sickle cell disease, certain skin cancers (particularly squamous cell carcinoma developing in a chronic wound), and long-term use of corticosteroids, which thin the skin and impair healing.
Some ulcers have mixed causes, particularly in older adults. A person might have both venous insufficiency and arterial disease contributing to the same wound, which complicates treatment because the standard approach for venous ulcers (compression) can be harmful when significant arterial disease is also present.
Risk Factors You Can and Can’t Control
Some risk factors for leg ulcers are fixed. Genetic predisposition, older age, female sex, family history of venous disease, and previous leg injuries or fractures all increase your chances. You can’t change those, but several modifiable factors also play a significant role.
Obesity is one of the strongest. A BMI over 30 is an established risk factor for chronic venous disease, and research in multiple populations has shown that higher BMI correlates with more severe disease. CVI is notably more common in obese individuals in industrialized countries. Prolonged sitting or standing, particularly in occupations that keep you in one position for hours, prevents the calf muscles from pumping blood back up the legs and worsens venous pressure over time. Physical inactivity has a similar effect. Smoking damages blood vessel walls and accelerates atherosclerosis, increasing the risk of arterial ulcers. Hormonal factors, including pregnancy and use of oral contraceptives, raise the risk of venous disease by affecting vein wall elasticity and blood clotting.
How Treatment Differs by Cause
Identifying the cause determines how the ulcer is treated. For venous ulcers, compression therapy is the cornerstone. Wrapping the leg with graduated compression bandages or stockings counteracts the high pressure in the veins and helps blood flow back toward the heart. Research shows that adding intermittent pneumatic compression (a device that rhythmically inflates and deflates around the leg) can more than double healing speed compared to standard compression bandages alone. Without compression, venous ulcers heal slowly and recur frequently.
Arterial ulcers require the opposite approach. Compression would further restrict an already limited blood supply and could worsen the damage. Treatment focuses on restoring blood flow, sometimes through procedures to open or bypass blocked arteries. Managing cholesterol, blood pressure, and smoking cessation are critical to preventing further arterial narrowing.
Diabetic ulcers require offloading pressure from the wound (often with specialized footwear or casts), tight blood sugar control to support healing, and regular monitoring because the lack of pain sensation means deterioration can happen silently. Inflammatory ulcers like pyoderma gangrenosum are treated with medications that calm the immune system rather than with compression or vascular procedures.
Because treatment for one type of ulcer can actively harm another, getting the correct diagnosis early is one of the most important steps in healing a leg ulcer. Ulcers that haven’t improved after several weeks of care, or wounds with unusual features like purple borders or rapidly expanding edges, often need specialist evaluation to rule out less common causes.