A foot ulcer typically appears as an open sore or wound on the foot, often round or oval, with edges that may be sharply defined or rimmed with thickened, callused skin. The wound bed itself can range from shallow and pink to deep and covered with yellowish or dark tissue, depending on the ulcer’s cause and how long it has been present. But foot ulcers vary enormously in appearance based on whether they stem from diabetes, poor circulation, vein problems, or prolonged pressure, and knowing what to look for at each stage can mean the difference between a wound that heals with basic care and one that leads to serious complications.
What the Earliest Signs Look Like
Foot ulcers rarely appear overnight. In most cases, the skin sends warning signals well before an open wound develops. In people with diabetes, one of the most common precursors is dry, scaly skin on the soles of the feet, often with visible cracks or fissures. This dryness results partly from nerve damage that reduces sweating. Thickened calluses, particularly under the ball of the foot beneath the metatarsal heads, are another hallmark of trouble brewing. These calluses build up because of abnormal pressure distribution, and if left untreated they can break down underneath, creating a hidden wound beneath an apparently intact surface.1PubMed. Xerosis and callus formation as a key to the diabetic foot syndrome: dermatologic view of the problem and its management
Other pre-ulcerative signs include blisters, areas of redness or discoloration that do not fade when pressed, bleeding within a callus, ingrown or abnormally thick toenails, and fungal infections between the toes. Clinical guidelines recommend treating all of these early signs aggressively, including removing callus, draining blisters when necessary, and addressing nail and fungal problems, because any break in the skin can become an entry point for a full ulcer.2Diabetes/metabolism research and reviews. IWGDF guidance on the prevention of foot ulcers in at-risk patients with diabetes
If you have diabetes and notice persistent redness, warmth, or a spot that feels different in texture from the surrounding skin, those are signals worth taking seriously even if the skin has not yet broken open. Because neuropathy dulls sensation, the visual check often matters more than how the foot feels.
Neuropathic Foot Ulcers
The most common type of foot ulcer in people with diabetes is neuropathic, caused by nerve damage that removes the normal pain signals that would tell you to shift your weight or stop walking on an injured area. These ulcers have a distinctive look. They typically appear on the bottom of the foot, particularly under the metatarsal heads (the bony prominences behind the toes) or on the undersides of the toes themselves.3BMJ. Diabetic foot ulcers The wound is often surrounded by a thick ring of callus, giving it a crater-like appearance.
A key visual clue is the surrounding skin. The neuropathic foot tends to be warm and well-supplied with blood, so the skin around the ulcer may look relatively healthy in color. Pulses in the foot are usually still palpable. However, the skin is often notably dry, and you may see cracks or fissures radiating away from the ulcer.3BMJ. Diabetic foot ulcers Plantar and heel ulcers frequently show a central depression with thickened borders and a ring of hardened skin around them.4Journal of Vascular Nursing. Literature-based visual and morphological characterization of diabetes-related foot lesions to inform high-fidelity three-dimensional anatomical modelling
Because there is little or no pain, neuropathic ulcers are often discovered only when the person notices drainage on their sock or sees the wound during a routine foot check. By the time someone spots one, it may already be moderately deep.
Arterial Ulcers
Arterial ulcers look quite different from neuropathic ones. They result from poor blood supply rather than nerve damage, and their visual hallmarks reflect that starved blood flow. Arterial ulcers are painful, tend to appear on the tips of the toes or over bony bumps like the ankle bone, and have a distinctive “punched out” shape with sharply defined borders. The wound bed is often pale, dry, and lacking the moist pink tissue you would expect in a healing wound.5PubMed Central. Venous and arterial leg ulcers
The skin surrounding an arterial ulcer gives additional clues. It tends to be cool to the touch, pale or shiny, and often hairless. The foot may look generally washed-out compared to the other foot, and pressing a toenail may show delayed refilling of color. If you elevate the foot, the pain typically gets worse and the skin may turn even paler, whereas hanging the foot over the side of the bed might relieve pain slightly and produce a dusky reddish color as gravity helps blood flow downward.5PubMed Central. Venous and arterial leg ulcers
Venous Ulcers and Pressure Injuries
Although venous ulcers are more commonly associated with the lower leg than the foot itself, they can extend to the ankle and foot area. Venous ulcers tend to be irregular in shape, relatively shallow, and surrounded by brownish discoloration of the skin caused by blood pigments leaking from congested veins. The wound bed is often moist, and early biopsies of venous ulcers reveal organized structures sometimes called fibrin cuffs along with inflammation and signs of red blood cell leakage into the surrounding tissue.6PubMed Central. Sequential changes in histologic pattern and extracellular matrix deposition during the healing of chronic venous ulcers Visually, you might notice a weepy, yellowish film over the ulcer bed alongside surrounding skin that looks stained or darkened.
Pressure ulcers on the foot, particularly on the heel, begin differently. The earliest visual stage is persistent redness on intact skin that does not blanch white when you press on it. In deeper skin tones, this might present as a persistent change in color, firmness, or temperature rather than obvious redness. From there, the wound can progress to blistering, shallow open sores, or in severe cases deep tissue injury that initially shows as a dark purple or maroon discolored area.7PubMed Central. Subepidermal moisture detection of heel pressure injury: The pressure ulcer detection study outcomes Heel pressure injuries are especially common in people who are bedridden or have limited mobility.
How Ulcers Are Graded by Severity
Clinicians use grading systems to describe how severe a foot ulcer looks and to guide treatment decisions. The most widely known is the Wagner classification, which runs from grade 0 through grade 5:
- Grade 0: The skin is still intact, but bony deformities or other risk factors put the foot at high risk for ulceration.
- Grade 1: A superficial ulcer limited to the skin surface.
- Grade 2: A deeper ulcer that extends through the full thickness of the skin into underlying tissue such as tendon or joint capsule.
- Grade 3: A deep ulcer with abscess formation or bone infection.
- Grade 4: Partial gangrene of the forefoot, meaning dead, blackened tissue on part of the toes or front of the foot.
- Grade 5: Extensive gangrene requiring major intervention.
This grading system has been validated as a predictor of outcomes; higher Wagner grades correspond to significantly higher rates of amputation.8PubMed Central. Wagner’s Classification as a Tool for Treating Diabetic Foot Ulcers: Our Observations at a Suburban Teaching Hospital A related system, the University of Texas classification, adds information about infection and blood supply and has shown that the risk of amputation rises sharply when infection is present, both alone and especially in combination with poor circulation.9Diabetes Care. A Comparison of Two Diabetic Foot Ulcer Classification Systems: The Wagner and the University of Texas wound classification systems
For a person looking at their own foot, the practical takeaway is that depth matters enormously. A shallow pink sore and a deep cavity exposing tendons or bone are both “ulcers,” but they sit at very different points on the severity spectrum. If you can see structures beneath the skin surface, or if the wound appears to go deeper than you expected when examined closely, seek professional evaluation promptly.
Visual Signs That an Ulcer Is Infected
Infection changes how a foot ulcer looks. The classic signs include increasing redness spreading outward from the wound edges, swelling, warmth, and discharge that may be cloudy, yellowish, greenish, or foul-smelling. You might also see red streaks radiating away from the ulcer, which suggest the infection is tracking along lymphatic channels.
In diabetic foot ulcers specifically, identifying infection by visual signs alone is tricky. Researchers have catalogued at least twelve different clinical signs used to assess infection in these wounds, but no single sign reliably predicts whether bacterial load is dangerously high. Even the combination of signs recommended by the Infectious Disease Society of America did not prove to be a strong standalone predictor of high bacterial counts in one study, which found the overall diagnostic accuracy was modest.10PubMed Central. Clinical signs of infection in diabetic foot ulcers with high microbial load This is partly because neuropathy and impaired blood flow can blunt the body’s normal inflammatory response, meaning a seriously infected diabetic foot ulcer may not look as angry or swollen as you would expect.
The bottom line for self-assessment: if you notice new or worsening redness around an ulcer, any discharge that was not there before, an unpleasant smell, or if the wound seems to be getting larger rather than smaller, assume infection is a possibility and get professional evaluation. Do not wait for all the classic signs to appear simultaneously.
Reading the Wound Bed
When you look directly at the base of a foot ulcer, the color and texture of the wound bed tell you a great deal about whether it is healing or in trouble. Healthy healing tissue, called granulation tissue, appears red or pink, has a bumpy or “cobblestone” texture, and may bleed slightly when touched. This is a good sign. As healing progresses further, new skin begins to grow inward from the wound edges; this epithelializing tissue appears as a thin, pinkish-white or silvery border creeping over the granulation tissue.
Unhealthy wound beds look different. Slough, a layer of dead cells and proteins, appears as yellow, white, or grayish stringy material clinging to the wound surface. Necrotic tissue, also called eschar, is harder and drier, typically black or dark brown, and represents tissue that has died completely. When the granulation tissue appears pale rather than a robust red, or when a wound simply stops making progress, that can point to problems like poor blood supply or hidden infection.11PubMed Central. Wound assessment
Modern wound care frameworks emphasize removing barriers to healing systematically, addressing non-viable tissue, controlling infection and inflammation, managing moisture balance, and monitoring the wound edge for signs that it is advancing inward or stalling.12British Journal of Nursing. TIME principles of chronic wound bed preparation and treatment If a wound has been present for weeks with no visible change in the edges, that stalled state is itself a visual sign that something is wrong.
When Bone Is Involved
One of the most serious complications of a deep foot ulcer is infection spreading to the underlying bone, a condition called osteomyelitis. Visually, the strongest clue is exposed bone visible at the base of the ulcer. But even when bone is not visible to the naked eye, it may be reachable with a sterile probe. In a study of infected foot ulcers in diabetic patients, probing that reached bone had a positive predictive value of 89% for osteomyelitis.13JAMA. Probing to Bone in Infected Pedal Ulcers: A Clinical Sign of Underlying Osteomyelitis in Diabetic Patients This is a clinical test rather than something you would do at home, but it underscores an important point: a deep ulcer that does not seem to be healing, especially one that is infected, may have bone involvement even if the wound looks moderate on the surface.
Other indirect visual signs that raise suspicion include a “sausage-like” swelling of a single toe, persistent redness over a bony area that will not resolve with wound care alone, and an ulcer that stays deep and open despite weeks of appropriate treatment.14PubMed Central. Osteomyelitis in the diabetic foot If you see any of these features, this is not a wound to manage on your own.
Where on the Foot Ulcers Tend to Appear
Location is one of the most useful clues for figuring out what type of ulcer you are dealing with. Diabetic neuropathic ulcers cluster on weight-bearing surfaces: the sole of the foot under the metatarsal heads, the tips and undersides of the toes, and the heel.15PubMed Central. Diabetic foot ulcer: A comprehensive review of pathophysiology and management modalities Arterial ulcers, by contrast, favor the tips of the toes and areas over bony prominences, particularly the outer ankle bone.5PubMed Central. Venous and arterial leg ulcers Pressure ulcers on the foot occur primarily on the heel, especially in immobile patients. Venous ulcers are most common around the inner ankle and lower leg.
A wound appearing in an unusual location, say on the top of the foot without a clear history of trauma, or on the shin rather than the sole, may suggest an atypical cause worth investigating further.
Ulcers That Are Not What They Seem
Not every chronic wound on the foot is a straightforward ulcer from diabetes, poor circulation, or pressure. Several conditions can mimic foot ulcers visually, and getting the diagnosis wrong means getting the treatment wrong.
One condition worth knowing about is Marjolin ulcer, a type of skin cancer that arises in areas of chronic scarring or long-standing wounds. It can resemble a non-healing ulcer but shows raised, irregular edges and may have a cauliflower-like or exuberant tissue growth that seems out of proportion. Pyoderma gangrenosum is another mimic; it typically begins as a blister or pustule at a site of minor injury and rapidly progresses into a painful, deep ulcer with a distinctive dusky-purple color and overhanging wound edges.16DermNet. Marjolin ulcer Some rarer vascular conditions, including those related to severe hypertension or calcium deposits in blood vessel walls, can produce painful ulcers with necrotic, blackened skin that can be mistaken for diabetic or arterial ulcers.17PubMed Central. Clinical characteristics and comorbidities of the most common atypical wounds in Northern Finland in 1996–2019: A retrospective registry study
The red flag for an atypical cause is usually a wound that does not respond to standard treatment the way you would expect, or one that looks different from the typical patterns described above. Any ulcer that keeps growing despite appropriate care, has unusual coloring, or develops raised or exuberant edges warrants a biopsy to rule out malignancy or an autoimmune process.
Challenges With Darker Skin Tones
Much of the standard teaching about wound and ulcer appearance was developed using images of lighter skin, which creates real problems for people with darker complexions. Redness, one of the cardinal signs of inflammation and infection, can be difficult or impossible to spot visually in deeply pigmented skin. Instead, you may need to rely on other cues: changes in skin temperature (the area feels warmer), changes in texture (tighter, shinier, or boggier than surrounding skin), increased pain or tenderness, and changes in color that appear as deepening of the skin’s natural tone rather than obvious redness.
Early-stage pressure injuries are particularly easy to miss in darker skin because the hallmark sign, non-blanching erythema, is defined by redness that does not fade with pressure. In darker tones, this may present as a purplish or ashen discoloration instead. Clinicians and patients alike should pay extra attention to areas over bony prominences and look for any patch of skin that feels or looks different from its surroundings, even if it is not red in the traditional sense.
Monitoring Your Own Feet With Photography
For people at risk of foot ulcers, particularly those with diabetes and neuropathy, regular visual inspection of the feet is one of the most important preventive habits. But checking the bottoms of your own feet is physically awkward, and many people with limited mobility or vision problems cannot do it well with a mirror alone.
Researchers have tested simple photographic monitoring systems where patients take pictures of the soles of their feet and transmit them to clinicians. One study using a prototype foot-imaging device found that important signs of diabetic foot disease, including ulcers and heavy callus buildup, could be reliably diagnosed from high-quality photographs, with agreement between photo-based and in-person assessments ranging from about 74% to 100% using the optimized version of the device.18PubMed. Assessment of foot disease in the home environment of diabetic patients using a new photographic foot imaging device A separate smartphone-based system, dubbed the “Foot Selfie,” showed that patients could capture diagnostic-quality images of the entire sole of both feet without help, allowing clinicians to make management decisions remotely.19PubMed Central. Initial Clinical Experience with a Simple, Home System for Early Detection and Monitoring of Diabetic Foot Ulcers: The Foot Selfie
Even without a dedicated device, taking regular photos of your feet with a smartphone and comparing them week to week can help you notice subtle changes, like a callus getting darker, a small crack widening, or a new area of discoloration. If you share those photos with your healthcare provider at routine visits, they can flag concerns you might not recognize on your own. For anyone who has already had one foot ulcer, this kind of vigilant monitoring is especially worthwhile, since recurrence rates are high and catching a new problem early dramatically improves the odds of a good outcome.