A diabetic foot ulcer is a serious complication arising from long-term high blood sugar levels, which damage the nerves and blood vessels. This condition results from peripheral neuropathy (nerve damage causing loss of sensation) and peripheral arterial disease (poor circulation that slows healing). Because of reduced feeling, a minor cut or blister can go unnoticed, progressing into an open wound that is difficult to repair. The lifetime risk of developing an ulcer is as high as 25% for a person with diabetes.
Identifying Early Warning Signs
Recognizing the earliest signs of tissue breakdown is essential before a visible ulcer forms. One subtle indicator is localized skin changes, such as unusual redness or swelling that does not subside after removing pressure. This redness frequently corresponds to a “hot spot” where the skin feels warmer than surrounding areas, signaling underlying inflammation.
Small blisters or patches of dry, cracked skin can also represent the beginning of an ulcer by compromising the skin’s protective barrier. Another common pre-ulcerative sign is the formation of a hardened callus, especially one that may hide underlying bleeding or discoloration. Because of neuropathy, these early visual clues are often not accompanied by pain, making daily foot inspection a fundamental part of preventative care.
Appearance of an Established Ulcer
Once the skin breaks and an established diabetic ulcer forms, its appearance varies based on its depth and health. A neuropathic ulcer often presents with a characteristic “punched-out” look, featuring a round or oval shape with well-defined, calloused edges. The depth can range from a superficial abrasion to a deep crater that exposes underlying tendons, joint capsules, or bone.
The color and texture of the wound base reveal its healing status and the presence of non-viable tissue. Healthy wounds show bright red, bumpy granulation tissue, which signifies new blood vessel formation. Conversely, the wound bed may contain yellow or gray, stringy material called slough, or a thick, black, leathery covering called eschar. Drainage (exudate) is also produced, which can be clear, bloody, or cloudy and thick, often staining socks or shoes.
Common Locations and Underlying Factors
Common Locations
Diabetic ulcers tend to form in specific areas of the foot that endure the highest mechanical stress during walking. The most frequent locations are the weight-bearing surfaces, particularly the ball of the foot, over the metatarsal heads, and the big toe. The heel and the tips of the toes are also common sites, especially if the person has foot deformities or wears ill-fitting footwear.
Underlying Factors
These locations are vulnerable because sensory neuropathy prevents the feeling of pain that would normally prompt weight shifting away from high pressure. Motor neuropathy can also cause small muscles in the foot to weaken, leading to deformities like hammer toes or claw toes that create abnormal bony prominences and pressure points. When poor blood flow is present, tissues cannot receive sufficient oxygen and nutrients, meaning a small wound cannot heal properly and breaks down into a chronic ulcer.
Signs of Advanced Infection
When a diabetic ulcer becomes infected, several visual signs indicate the severity of the problem. One noticeable indicator is a foul odor coming from the wound, suggesting a high bacterial load. The skin around the ulcer may display rapidly spreading redness, which is a sign of cellulitis, an infection of the deeper layers of skin and soft tissue.
The wound drainage will often change from clear to a thick, cloudy, or discolored pus (yellow, green, or brown). In the most severe cases, tissue may start to die due to lack of blood supply or overwhelming infection, leading to gangrene. This appears as dark purple, black, or mummified tissue, often accompanied by systemic symptoms like fever and chills, indicating the infection is spreading.