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

A diabetic foot ulcer is an open sore or wound on the foot, often on the sole or the toes. It's one of the most serious foot problems diabetes can cause. A 2023 review estimated that about 1.6 million people in the United States get one each year, and that these ulcers come before 80% of diabetes-related amputations (Armstrong and colleagues, 2023). The same review found that several steps lower the risk: shoes that take pressure off vulnerable spots, checking foot temperature, and treating early warning signs.

Why Diabetes Threatens the Feet

The most common causes of foot ulcers are nerve damage, injury, changes in foot shape, high pressure on one spot and poor circulation (Frykberg, 2002). Often, several of them work together.

Nerve damage (neuropathy). It's common. A Cochrane review notes that it affects about 1 in 10 people when diabetes is diagnosed and 4 to 5 in 10 after ten years (Callaghan and colleagues, 2012). When the nerves in your feet stop working well, you can step on a tack, rub a blister or burn your foot and not feel it. Nerve damage can also cut down on sweating. The skin then dries out, and dry skin can crack and turn into an ulcer (Oe and colleagues, 2025).

Poor circulation (peripheral artery disease). Less blood reaches the feet, so small injuries heal slowly. It often causes no symptoms at all. Calf pain that comes on with walking and eases with rest (claudication) is the classic sign, but only about 1 in 10 people with the condition have it (Firnhaber and Powell, 2019). That's why a diabetic foot exam includes checking the pulses in your feet. Sometimes it also includes a simple test that compares blood pressure at the ankle and the arm.

Infection. Once the skin is open, germs can get in. About half or more of diabetic foot ulcers become infected (Armstrong and colleagues, 2023). An infection can spread to deeper tissue and to the bone.

The Warning Signs Before an Ulcer Develops

An ulcer often starts as a smaller problem that you can see or feel. Doctors call these pre-ulcer signs, and treating them lowers the risk of an ulcer (Armstrong and colleagues, 2023). Watch for the following.

• Color changes. Redness that doesn't fade after your shoes and socks come off, redness around a callus, blister or crack, or skin that looks dark, purple or pale.
• Warm or cold spots. A spot that feels warmer than the same spot on the other foot can mean inflammation. A foot that feels cold can mean poor blood flow.
• Calluses. Thick skin on the sole marks a high-pressure spot. A callus with dark spots or dried blood under it can be hiding a sore.
• Blisters, cuts or cracks. Any break in the skin, however small, lets germs in.
• Swelling. Swelling in one foot can mean infection, a circulation problem or Charcot foot.
• Drainage or odor. Fluid on your sock, pus, or a bad smell from the foot.
• A change in foot shape. A new bump, a collapsing arch, or one foot that looks different from the other.

Research backs up two of these signs in particular. In one study of people with nerve damage, an ulcer was far more likely to form under a callus (Murray and colleagues, 1996). It was most likely of all where an old ulcer had been. Checking foot temperature, then resting the foot when one side ran hot, also lowered the number of ulcers in studies (Armstrong and colleagues, 2023). The international guideline suggests that doctors consider teaching higher-risk patients to track their foot temperature (Bus and colleagues, 2024).

A foot that turns red, hot and swollen, often without an open sore, can be Charcot foot (Botek and colleagues, 2010). In Charcot foot, the bones and joints of a numb foot weaken and can collapse. It's serious and can threaten the limb (Rogers and colleagues, 2011). It's also easy to mistake for an infection, so it needs prompt care to keep the foot working.

The Daily Foot Check

Check both feet every day: the tops, the soles, the heels and between the toes. Use a mirror, or ask someone to look at your soles. Look for any of the warning signs above, plus fungus between the toes or on the nails and ingrown nails. It takes only a few minutes, and it helps you catch problems your feet may not feel. The international guideline recommends teaching people at risk how to care for their feet (Bus and colleagues, 2024). Here's our daily foot-care checklist.

Key Prevention Strategies

Blood sugar control. Keeping your blood sugar in your target range helps protect your nerves. In a Cochrane review, tighter control clearly lowered the risk of nerve damage in type 1 diabetes. In type 2 diabetes the benefit was smaller and less certain, and tighter control raised the risk of dangerously low blood sugar (Callaghan and colleagues, 2012). Work with your doctor on a target that's safe for you.

The right shoes. Don't go barefoot, even at home, and check inside your shoes before you put them on. The international guideline advises people at risk not to walk without proper foot protection (Bus and colleagues, 2024). For people at moderate or high risk, it recommends well-fitting therapeutic shoes. A 2023 review reported that shoes designed to take pressure off vulnerable spots lowered the rate of ulcers compared with usual care (Armstrong and colleagues, 2023). These shoes usually have extra depth for a custom insert, a smooth lining without seams, and closures you can adjust for swelling. Custom orthotics can move pressure away from high-risk spots.

Skin and nail care. Moisturize your feet every day, but not between the toes. Urea creams can help relieve dry feet (Oe and colleagues, 2025). Trim nails straight across. Treat athlete's foot and nail fungus early. Never use sharp tools, chemical corn removers or heating pads on your feet.

Regular foot exams. Exams catch problems you can't feel. The international guideline recommends a yearly screening for people at very low risk and more frequent checks for everyone at higher risk (Bus and colleagues, 2024). At a visit, we test your feeling and circulation and look at your shoes. See how we handle diabetic foot care and neuropathy.

How a Foot Ulcer Is Treated

If an ulcer does form, treatment focuses on removing dead tissue, taking pressure off the wound, and treating poor circulation and infection (Armstrong and colleagues, 2023). You may need a special shoe or boot while it heals. Care often involves a team: your podiatrist, your primary doctor and, when needed, infection and vascular specialists. That kind of team care is linked with fewer major amputations (Armstrong and colleagues, 2023). Learn more about our wound care.

Healing takes time. A 2023 review estimated that 30% to 40% of ulcers heal within 12 weeks, and that 42% come back within a year after healing (Armstrong and colleagues, 2023). That's why protective shoes and regular checkups continue after a wound closes.

When to Seek Immediate Help

Don't wait for your next appointment. Call us right away if you notice any of these.

• An open sore or a wound that isn't healing
• Redness or warmth spreading from a wound
• Drainage or pus
• Fever or chills
• A sudden change in the color of your foot
• A foot that turns red, hot and swollen
• New pain in a foot that has been numb
• Any injury that breaks the skin

If you have fever, chills or spreading redness and can't reach us, go to urgent care or an emergency room. Prompt treatment can often keep a small wound from getting worse (Frykberg, 2002).

Diabetic foot care is a lot of small habits: daily checks, good shoes and regular visits. Together, they add up to real protection for your feet. If your feet feel numb or tingly, here's why feet go numb and what to do.