Diabetic Foot Ulcer Warning Signs: What to Watch For and How to Prevent Them

Diabetic foot ulcers are the most feared complication in diabetic foot care — and for good reason. In the United States, approximately 15–25% of people with diabetes will develop a foot ulcer during their lifetime. These ulcers are the leading cause of non-traumatic lower extremity amputations. But here's the critical fact: the vast majority are preventable with proper surveillance, daily self-care, and early intervention.

Understanding the warning signs — the subtle changes that precede an ulcer — is your best defense.

Why Diabetes Threatens the Feet

Diabetes creates a perfect storm for foot problems through three interconnected pathways.

Peripheral neuropathy — nerve damage from chronically elevated blood sugar — affects approximately 50% of people with diabetes. It manifests as loss of protective sensation: the ability to feel pain, pressure, and temperature changes in the feet. Without this warning system, injuries go unnoticed. A patient might step on a tack, develop a shoe blister, or have a pressure sore forming — and not feel any of it.

Peripheral vascular disease — reduced blood flow to the extremities — impairs the delivery of oxygen, nutrients, and immune cells needed for tissue maintenance and wound healing. The feet, being the farthest point from the heart, are most affected. Reduced circulation means small injuries heal slowly and are more susceptible to infection.

Immune dysfunction from diabetes impairs the body's ability to fight infection. Hyperglycemia directly suppresses white blood cell function. Infections that would be minor in a healthy person can become limb-threatening in a diabetic foot.

The Warning Signs Before an Ulcer Develops

Ulcers don't appear overnight. They develop through a predictable sequence of warning signs — and recognizing these early stages is where prevention happens.

Color changes. Areas of redness that persist after removing pressure (shoes, socks) suggest excessive pressure or early tissue damage. Redness around a callus, blister, or skin break is particularly concerning. Dark or purplish discoloration may indicate ischemia (insufficient blood flow).

Temperature differences. One area of the foot that feels noticeably warmer than the surrounding skin suggests inflammation or infection. An area that feels abnormally cool may indicate compromised blood flow. A simple daily temperature check — feeling different areas of both feet — can catch problems early.

Callus buildup. Thick calluses on the bottom of the foot indicate areas of excessive pressure. Under a callus, the tissue can break down without being visible from the surface. A callus with discoloration (dark spots or blood staining underneath) is a pre-ulcerative lesion that needs professional attention.

Blisters or skin breaks. Any break in the skin of a diabetic foot — no matter how small — is a potential entry point for infection. Friction blisters from ill-fitting shoes are a common initiating event.

Swelling. Localized swelling can indicate infection, Charcot arthropathy (a serious bone and joint condition), or vascular problems.

Drainage or odor. Any discharge from the foot — clear fluid, blood, or especially pus — warrants immediate evaluation. Foul odor from a wound often indicates anaerobic bacterial infection, which can be limb-threatening.

Changes in foot shape. Gradual changes in the shape of the foot — new prominence of bones, collapse of the arch, or swelling that makes one foot look different from the other — can indicate Charcot neuroarthropathy, a progressive destruction of bones and joints that occurs in neuropathic feet.

The Daily Foot Check

Every person with diabetes should perform a daily visual inspection of both feet — every surface, between every toe. Use a mirror or ask a family member to help check the bottoms. You're looking for: cuts, blisters, cracks, or sores; redness, swelling, or warm areas; calluses with discoloration; changes in skin color or texture; fungal infections (between toes or on nails); and ingrown toenails.

This takes less than two minutes and is the single most effective habit for preventing ulcers.

Key Prevention Strategies

Blood sugar control is foundational. Maintaining A1C as close to target as possible slows progression of neuropathy and vascular disease. Every point of A1C reduction meaningfully decreases complication risk.

Proper footwear is non-negotiable. Shoes should be fitted at the end of the day when feet are largest. Avoid going barefoot — even at home. Inspect the inside of shoes before putting them on (checking for foreign objects or rough seams). Diabetic shoes with extra depth accommodate foot deformities and reduce pressure. Custom orthotics redistribute pressure away from vulnerable areas.

Skin and nail care. Moisturize daily (but not between the toes, where moisture promotes fungal growth). Trim toenails straight across — or better yet, have them trimmed professionally. Treat fungal infections promptly, as they compromise skin integrity. Never use sharp instruments, chemical corn removers, or heating pads on diabetic feet.

Regular podiatric care. Professional foot exams at regular intervals allow early detection of problems that a patient with neuropathy might not feel. Callus debridement, nail care, vascular assessment, and neuropathy screening are all part of comprehensive diabetic foot management.

When to Seek Immediate Help

Don't wait for your next scheduled appointment if you notice: any open sore or wound that isn't healing, redness or warmth spreading from a wound, drainage or pus, fever or chills, sudden change in foot color, new pain in a previously numb foot (which paradoxically can indicate worsening neuropathy or acute Charcot), or any injury to the foot that breaks the skin. Early treatment of a small wound can prevent it from becoming a limb-threatening emergency.

Diabetic foot care might seem like a lot of small steps — daily inspections, proper shoes, regular checkups — but those small steps add up to the most powerful prevention strategy we have. The goal is to keep your feet healthy, intact, and functional for a lifetime.