Signs of Wound Infection
Reviewed by Andrew Schox, BSc(Hons) PGradDipPod MPod, October 2026
Infection happens when bacteria (germs) get into a break in the skin. In people with diabetes, a foot wound is judged to be infected when at least two signs are present: pain, tenderness, warmth, redness, hardness around the wound, or pus. Roughly 50 per cent of foot ulcers (open sores) in people with diabetes become infected. Numb feet and poor blood flow can hide the signs, so a wound that isn't healing still needs checking. Infections can become serious quickly, but early treatment lowers the risk of a hospital stay and amputation.
What is it?
A wound infection happens when bacteria (germs) get into a break in the skin and cause harm. This page is about foot wounds in adults with diabetes, which is where infection is most often a worry. If you are caring for a child, or have a different kind of wound, get advice from a health professional early.
Podiatrists and doctors mainly judge infection by what they can see and feel. A foot wound is treated as infected when at least two of these are present: pain, tenderness, warmth, redness, hardness around the wound, or pus (thick fluid made by an infection). Infections are then graded as mild, moderate or severe.
Some changes are part of normal healing. A healing wound can have some redness, slight swelling and a light-yellow discharge, and this doesn't always mean infection. But the reverse is also true: having none of the classic signs doesn't rule infection out. A numb foot or poor blood flow can hide the signs, so a wound that looks mild or doesn't hurt, but isn't getting better, still needs to be checked.
What can cause it?
The most common cause is an infection of the soft tissue (the skin and the layers just beneath it) around a wound. Most of these infections involve more than one type of bacteria, and staphylococci are the most common. If you have already had antibiotics, or the infection has been there a long time, other types of bacteria are often involved as well.
An infection near the surface can spread deeper:
- Bone infection (osteomyelitis): an infection in a wound can reach the bone. It is harder to diagnose and treat than a skin infection, and often needs surgery, a long course of antibiotics, or both.
- Abscess: a pocket of pus deep in the foot. It is a sign of a moderate infection, and an abscess that isn't drained is a common reason an infection doesn't respond to treatment.
- Poor blood supply: this can make any infection more severe. Dead tissue or poor blood flow also lets other types of bacteria take hold.
Not every red or sore wound is infected. Normal healing can look a little like early infection. If an infection doesn't respond to treatment, your team will also think about other causes, such as a foot condition called Charcot foot.
Who gets it?
People with diabetes are at the greatest risk. Diabetes makes foot ulcers more likely, slows healing and makes infection more likely. About 6.3 per cent of people with diabetes have a foot ulcer. Roughly 50 per cent of these ulcers become infected. Across a lifetime, 19 to 34 per cent of people with diabetes get a foot infection. These are two different measures, so they can't be added or compared directly.
Several things raise the risk:
- Nerve damage: if your foot is numb, you may not feel a pebble in your sock or a blister. The same spot can keep being damaged without you knowing.
- Poor blood flow: skin needs good circulation to heal and fight infection.
- Foot shape changes (deformity): these can cause pressure spots and slow healing.
- Hard skin on or around a sore: it can hold bacteria and delay healing.
People with foot ulcers also tend to be older, to have had diabetes for longer, and to have high blood pressure, eye damage from diabetes or a smoking history.
How is the cause found?
Your podiatrist will look at the whole foot, not just the wound. They will check for the signs of infection, check the circulation (including whether they can feel the pulses in your foot) and test your feeling. They will usually grade how serious the infection is, which helps decide whether you need to go to hospital, have scans or have surgery.
If an infection is suspected, a sample from the wound is best taken before antibiotics start. A sample of tissue taken after dead tissue has been cleaned away is preferred.
If bone infection is suspected, a plain X-ray is usually done first. An MRI scan is the most accurate scan for bone infection. A small sample of bone (a biopsy) is the most reliable way to confirm it and to find out which bacteria are involved.
Treatment
Treatment usually combines wound care, taking pressure off the area, cleaning away dead tissue, checking and treating the blood supply, good blood sugar control and, when needed, antibiotics. The sooner it starts, the better.
Looking after it at home
Until you are seen at the podiatry clinic, cover the wound with a suitable dressing and keep it dry. Take as much pressure off the area as you can, for example by changing your footwear or by not putting weight on that foot.
Don't cut or pick at hard skin around the wound yourself. Your podiatrist can remove it safely.
Treatment from your podiatrist
Your podiatrist will remove hard skin and dead tissue with a sterile blade. This lets the wound heal from the base upwards and removes a place where bacteria can hide. They will also set up ways to keep pressure off the wound, such as special footwear or protecting the area so you don't put weight on it, and they will choose a suitable dressing.
They will check your circulation early. If they can't feel the pulses in your foot, they will refer you to a vascular surgeon (a doctor who treats blood vessels).
A doctor will prescribe antibiotics if there are signs of an infection in the soft tissue or bone. The choice depends on how severe the infection is and how long you have had the wound. Your treating team should review early whether the treatment is working. Good blood sugar control is also part of treatment.
Other options
If an infection isn't improving, your team will go back over the basics. They will check for another cause, such as Charcot foot, and whether there is a pocket of pus that needs draining. They may repeat the samples, and they will make sure pressure relief, wound care and blood supply are being looked after. They may also ask an infection specialist for advice, particularly if the infection isn't improving on antibiotics, if you can't take the usual antibiotics, or if it keeps coming back.
People at risk of resistant bacteria, or with a long-standing, previously treated or severe infection, usually need broader antibiotics.
Most foot infections need some surgery, from minor cleaning of the wound to larger operations. A severe infection needs urgent surgery to drain pus and remove dead tissue, and sometimes a toe or part of the foot has to be removed. If the foot has a poor blood supply, a procedure to restore the blood flow may be needed. Care from a team of foot specialists working together improves results.
Will it get better?
A foot infection in a person with diabetes is serious, and it can become worse very quickly. About 15 to 20 per cent of moderate to severe infections eventually lead to the loss of part of the leg or foot (a lower-limb amputation). Up to 20 per cent of infected ulcers need a hospital stay.
Early treatment lowers these risks, and each day's delay in getting help matters. If you suspect an infection, contact your podiatrist or GP as soon as you can. If your usual service is closed, use an urgent advice service rather than waiting until the next working day, especially if things are getting worse.
Preventing it
Check your feet regularly. If you can't see the soles easily, ask someone to help or use a mirror. Contact your podiatrist or GP early if a cut, blister or bruise hasn't started to heal after a few days, if the skin turns red, warm or painful, or if you see a callus (hard skin) with dried blood inside it. That can be the first sign of a wound under the callus.
If you have diabetes, don't cut corns or calluses yourself, and don't use over-the-counter corn removal products. They can damage the skin and lead to infection. If you go to a salon for a pedicure, take your own nail tools, and ask your podiatrist or GP what else you can do to protect your feet there.
When to see a podiatrist
Book an appointment if
Book an appointment with your podiatrist soon if you have diabetes and a cut, blister or bruise on your foot hasn't started to heal after a few days, the skin on your foot has become red, warm or painful, or you have a callus with dried blood inside it. Book too if a wound isn't getting better with care, even if it looks mild or doesn't hurt, because a numb foot or poor blood flow can hide infection.
Seek prompt assessment if
Call your local emergency number if you have a foot wound or infection and you also feel very unwell, with confusion or slurred speech, severe shivering or extreme muscle pain, feeling unusually cold, passing little or no urine, severe breathlessness, mottled, blue, grey, pale or discoloured skin, or a feeling that you might die. This could be sepsis, so don't wait for all of these signs to appear. Call your local emergency number too if your leg, foot or toes suddenly turn cold and pale or blue, with pain or numbness, or if you suddenly can't move your leg or foot.
This needs urgent medical assessment: see your GP or podiatrist today, or go to an urgent care clinic or the nearest emergency department. Do this if you have:
- an open sore (ulcer) on your foot
- a fever or chills with a wound
- redness spreading out from the wound, or red streaks running up the skin from it
- pus building up in or around the wound
- an infection that is getting worse, or isn't improving, even though you are taking antibiotics
- pain in your foot that is increasing even when you are resting
- a wound that is getting worse, or skin around it that is turning dark or black
A foot infection that turns black and smelly can be a sign of gangrene (dead tissue), so call your health care provider right away. If your usual service is closed, use a health advice phone line if there is one where you live, or an after-hours GP, rather than waiting until the next working day.
Frequently asked questions
Do all infected wounds need antibiotics?
Antibiotics are for wounds with signs of an infection in the soft tissue or bone. A wound without these signs doesn't need them. Your doctor chooses the antibiotic, the dose and how long you take it, and checks early that it is working.
Can a swab tell me if my wound is infected?
Not on its own. All open wounds carry some bacteria, so a positive result is hard to interpret. Infection is judged mainly from how the wound and foot look and feel. A sample is used to find out which bacteria are involved and so choose the right antibiotic.