Leg ulcers: why they happen and what it takes to heal them

A leg ulcer is a break in the skin of the lower leg that refuses to heal within a few weeks. It is less a disease in itself than a signpost: somewhere upstream, something is preventing the skin from repairing itself, and until that something is found and treated, the ulcer tends to stay.

That single idea explains most of what follows — because the commonest mistake in leg ulcer care is to treat the hole in the skin while ignoring the reason it exists.

The three big causes of leg ulcers

Venous ulcers account for the majority. When the one-way valves in the leg veins leak — a condition called chronic venous insufficiency — blood pools in the lower leg and the pressure inside the veins stays abnormally high, even at rest. Over years, that pressure damages the skin from within: it darkens, hardens and itches, and eventually breaks down, often after a trivial knock.

Arterial ulcers are the reverse problem. Narrowed or blocked leg arteries — peripheral arterial disease — mean the tissues receive too little oxygen-rich blood to repair even minor damage. The skin is not being flooded; it is being starved.

Mixed and diabetic ulcers make up much of the rest. Plenty of people have a degree of both venous and arterial disease in the same leg. Add diabetes and the picture changes again: nerve damage lets injuries go unnoticed, and impaired healing and infection risk make the diabetic foot a field of wound care in its own right.

How the causes look different

Each cause leaves its own fingerprints:

• Location. Venous ulcers favour the inner side of the lower calf and ankle — the so-called gaiter area. Arterial ulcers appear at the far ends of the circulation: the toes, the heel, the front of the shin. Diabetic ulcers sit at pressure points — the ball of the foot, under a callus, over a deformed joint.
• Edges and base. Venous ulcers tend to be shallow and irregular, with a wet, weeping base. Arterial ulcers look “punched out” — smaller, deeper, sharply edged, with a pale or dark, dry base.
• Pain pattern. Venous ulcers ache after prolonged standing and ease with elevation. Arterial ulcers do the opposite: they hurt more at night or when the leg is raised, and hanging the foot out of bed brings relief, because gravity helps blood reach it. Diabetic ulcers with nerve damage often hurt far less than their appearance suggests — which is exactly the danger.

These are patterns rather than rules, and mixed pictures are common. That is why formal assessment matters more than bedside guesswork.

Why dressings alone cannot heal them

A dressing does a genuinely useful job: it keeps the wound clean and moist, absorbs fluid and protects new tissue. What it cannot do is lower the pressure in a leaking vein or restore flow through a blocked artery. An ulcer whose cause is untreated can be dressed diligently twice a week for a year and end the year exactly where it began — I have met many patients for whom that is not a hypothetical.

How I assess a leg ulcer

Two tests answer most of the question.

A duplex ultrasound scan maps the veins and arteries of the leg and shows the blood flowing through them in real time — which valves are leaking, which segments are narrowed or blocked. It takes about twenty minutes, involves no needles or radiation, and in my clinic it is done during the consultation.

The ankle–brachial pressure index (ABPI) compares the blood pressure at the ankle with the pressure at the arm. In a healthy leg the two are roughly equal. A clearly lower ankle pressure signals arterial disease — and, just as important, warns that compression bandaging must be modified or avoided, because compressing a poorly supplied leg can make matters worse.

Treatment follows the cause

For venous ulcers, once arterial disease has been excluded, graduated compression — firm bandaging or stockings, snuggest at the ankle — is what international vascular guidelines consistently recommend first, because it directly counters the raised pressure in the veins. Treating the leaking vein itself, often with a minimally invasive procedure under local anaesthesia, addresses the underlying cause and reduces the chance of the ulcer returning once it has healed.

For arterial ulcers, the priority is restoring blood flow — usually with angioplasty, reopening the artery from within using a balloon and sometimes a stent, occasionally with bypass surgery. Until flow is restored, no dressing can outrun the lack of supply.

For diabetic ulcers, several things happen in parallel: pressure is offloaded from the wound, infection is controlled, blood sugar is optimised and the circulation is checked — because a proportion of diabetic ulcers have an arterial component that also needs treating.

As for timescales: with the cause properly treated, most venous ulcers heal over weeks to months, with larger and longer-standing ulcers at the slower end. Healing is rarely a straight line, and the work does not end when the skin closes — skin that has ulcerated once remains vulnerable, and for venous disease, continuing with compression stockings substantially reduces the risk of recurrence.

When to see a doctor promptly

Any wound on the lower leg that has not clearly improved within two weeks deserves proper assessment — not another month of the same dressing. Seek review urgently if there is spreading redness or warmth, fever, blackened tissue, rapidly worsening pain, or any foot wound in a person with diabetes. And if an ulcer has already been present for months, that is not a reason to wait longer — it is all the more reason to find the cause now.