On a foot, the usual first warning sign can be missing. Diabetic ulcers are often painless, because of decreased feeling in the feet. If pain is the sign you are waiting for, you may wait a long time. You have to check by eye and by hand instead.
For a foot ulcer, contact your provider if you have any of these signs of infection: redness, increased warmth, or swelling around the wound; extra drainage; pus; odor; fever or chills; increased pain; or increased firmness around the wound.
Increased firmness is the one most often missed, because you feel it rather than see it. Pressing gently around the wound, and comparing with yesterday, is a different check from looking at it.
Color is a separate warning. Also contact your provider if your foot ulcer is very white, blue, or black. That is a reason to make contact whether or not any sign of infection is present.
Foot wounds are taken this seriously for a reason. Diabetes can damage the nerves and blood vessels in your feet. As a result, your feet are more likely to get injured and may not heal well if they are injured. Foot ulcers are a common reason for hospital stays for people with diabetes. That is why a new sign on a foot wound is worth a phone call rather than a wait.