A diabetic foot ulcer is an open sore or wound that occurs in approximately 15 percent of patients with diabetes and is commonly located on the bottom of the foot. Of those who develop a foot ulcer, six percent will be hospitalized due to infection or other ulcer-related complication. Ulcers can look like blisters, cuts, cracks, sores, redness, white spots or areas, thick calluses, discoloration, or other changes. Don't rely on pain; even feeling more warmth or cold than usual can be a sign that you have an open wound on your skin, and it's possible that you may feel nothing at all.