Infection of an Open Wound

Can open wounds cause infection?

Yes. Intact skin is the body's main barrier against bacteria. Any open wound, from a scraped knee to a surgical cut, gives bacteria living on your skin or in the environment a way in. Most wounds heal without infection because the immune system clears small numbers of germs. Infection develops when too many bacteria get in, or when the body's defenses are weakened.

Wounds most likely to become infected:

• Bites from animals or humans, which inject mouth bacteria deep into tissue
• Puncture wounds, such as stepping on a nail, which are hard to clean
• Dirty wounds contaminated with soil, rust, feces or saliva
• Crush injuries and wounds with dead tissue
• Wounds left uncleaned or closed with debris inside
• Wounds on the feet and legs, where blood flow is weaker

Signs of an infected wound

Some redness, swelling and tenderness in the first 48 hours is normal inflammation. Infection is more likely when things get worse instead of better after day 2 or 3.

Other warning signs include red streaks spreading from the wound (lymphangitis), tender lumps in the armpit or groin, and wound edges that open up.

Types of wound infection

• Local wound infection: confined to the wound and its edges.
• Cellulitis: infection spreading through the skin and the fat beneath it, with a growing red, warm patch. See cellulitis.
• Abscess: a walled-off pocket of pus that feels like a tender, fluctuant lump. It usually needs draining. See abscess.
• Necrotizing fasciitis: a rare, fast-spreading infection of deep tissue. It causes severe pain, then skin discoloration and blistering, and needs emergency surgery.
• Osteomyelitis: infection reaching the bone, a risk with deep wounds, foot ulcers in diabetes and open fractures.
• Sepsis: the body's extreme reaction to infection in the bloodstream.
• Tetanus: caused by toxins from Clostridium tetani in soil. It causes muscle stiffness and spasms, and is prevented by vaccination.

Risk factors

• Diabetes, especially with poor blood sugar control or numb feet
• Poor circulation, smoking and older age
• A weakened immune system (chemotherapy, steroids, HIV, transplant medicines)
• Obesity and malnutrition
• Swelling (edema) of the limb
• Foreign material left in the wound, such as glass, gravel or splinters

Diagnosis

Most wound infections are diagnosed by looking at the wound and asking how it happened. The clinician may:

• take a swab of pus to identify the bacteria and which antibiotics work, including whether it is MRSA
• order an X-ray or ultrasound to look for a foreign body, an abscess or bone involvement
• do blood tests (white cell count, CRP, blood cultures) if you have fever or seem unwell
• mark the edge of the redness with a pen to track whether it spreads

Treatment

Medical treatment

• Cleaning and debridement: washing the wound and removing dead tissue and debris.
• Opening and draining any pus collection. Stitches may be removed to let a surgical wound drain.
• Antibiotics: tablets for spreading redness or high-risk wounds such as bites. Intravenous antibiotics in hospital for severe infection, sepsis or failure to improve within 48 hours.
• Tetanus booster if you are not up to date.
• Surgery for necrotizing infections or infected bone.

Take the full antibiotic course as prescribed. The redness should stop spreading within 24 to 48 hours. If it does not, go back.

Home care for a mildly infected wound

These steps suit only a small, mild infection without fever or spreading redness, or alongside medical treatment:

• Wash your hands, then rinse the wound with clean running water for several minutes. Mild soap can be used on the skin around it.
• Avoid hydrogen peroxide or iodine for repeated cleaning, as they damage healing tissue.
• Apply a thin layer of petroleum jelly or an antibiotic ointment and a clean, non-stick dressing.
• Change the dressing daily or whenever it is wet or dirty.
• Raise an infected arm or leg to reduce swelling.
• Use acetaminophen (paracetamol) or ibuprofen for pain, following the label dose.
• Do not squeeze pus out or cut into the wound yourself.

Preventing wound infection

• Clean every wound promptly under running water and remove visible dirt.
• Cover it with a clean dressing until it has sealed.
• Get deep, gaping, dirty or bite wounds checked within hours. Wounds closed within about 6 to 8 hours (longer on the face) heal best.
• Keep tetanus vaccination up to date: a booster every 10 years, or after 5 years for a dirty wound.
• Check your feet daily if you have diabetes.

Frequently asked questions

Can open wounds cause infection?

Yes. Any break in the skin lets bacteria in. Most small wounds heal without trouble, but dirty wounds, bites, punctures and wounds in people with diabetes or poor circulation are more likely to become infected. Cleaning the wound well and keeping it covered lowers the risk.

How do I know if my wound is infected?

Look for redness that spreads, increasing pain, warmth, swelling, pus and a bad smell, especially after the second or third day. Fever, red streaks or swollen glands mean the infection is spreading and needs medical treatment the same day.

Will an infected wound heal on its own?

A very mild infection limited to the wound edge may settle with careful cleaning and dressings. Spreading redness, pus, fever or red streaks will not reliably clear without antibiotics or drainage, and can spread to the blood. If it is not clearly improving within a day or two, see a doctor.

What does wound pus look like?

Pus is thick and cloudy, and usually yellow, green or brown. It often smells unpleasant. Thin, clear or pale yellow fluid in the first few days is normal and is not pus. Read more about wound discharge and what each color means.

How long does it take for a wound infection to clear?

With the right antibiotics, redness should stop spreading within 1 to 2 days and improve clearly within 3 to 5 days. Full healing of the wound itself may take 1 to 3 weeks or longer, depending on size and depth.