Your skin is a natural barrier against infection. Even with precautions to prevent infection, any surgery that causes a break in the skin can lead to an infection. Doctors call these infections surgical site infections (SSIs) because they happen on the part of the body where the surgery took place. If you have surgery, the chances of developing an SSI are about 2% to 4%.

If an SSI happens, it's typically within 30 days after surgery. The CDC describes three types of SSIs:

• Superficial incisional SSI. This infection occurs just in the area of the skin where the incision was made.
• Deep incisional SSI. This infection happens beneath the incision area in the muscle and the surrounding tissues.
• Organ or space SSI. This type of infection can be in any area of the body other than skin, muscle, and surrounding tissue that was involved in the surgery. It includes a body organ or a space between organs.

The symptoms of any SSI may include redness, delayed healing, fever, pain, tenderness, warmth, or swelling. These are the other signs of specific types of SSI:

• A superficial incisional SSI may produce pus from the wound site. Samples of the pus may be grown in a culture to find out which germs are causing the infection.
• A deep incisional SSI may also produce pus. The wound site may reopen on its own, or a surgeon may reopen the wound and find pus inside it.
• An organ or space SSI may show pus coming from a drain that's placed through the skin into a body space or organ. A collection of pus, called an abscess, may be seen when the surgeon reopens the wound or in special X-ray studies.

Infections after surgery are caused by germs. The most common include the bacteria Staphylococcus, Streptococcus, and gram-negative bacilli. Germs can infect a surgical wound in various ways. These include:

• The touch of a contaminated caregiver or surgical instrument.
• Germs in the air.
• Germs that are already on or in your body and then spread into the wound.

Your risk for an SSI depends on the type of surgical wound you have. They include:

• Clean wounds. These are not inflamed or contaminated. They don't involve operating on an internal organ with any bacteria normally inside it.
• Clean-contaminated wounds. These have no evidence of infection at the time of surgery. But they do involve operating on an internal organ that has some bacteria in it.
• Contaminated wounds. These involve operating on an internal organ when contents from the organ spill into the wound.
• Dirty wounds. These are wounds that have a known infection at the time of the surgery.

Other risk factors for SSIs include:

• Having surgery that lasts more than 2 hours
• Having other medical problems or diseases
• Being an older adult
• Being overweight
• Smoking
• Having cancer
• Having a weak immune system
• Having diabetes
• Having emergency surgery
• Having abdominal surgery

If you're having surgery, ask your doctor what you can do to reduce your risk for an SSI. It's important to stop smoking before surgery. And tell your surgical team about your medical history, especially if you have diabetes or another chronic illness. Avoid shaving in the skin area that the surgeon is planning to operate through.

No matter how curious they are, loved ones should not touch your wound or surgical site. Carefully follow your doctor's instructions about wound care after surgery. Contact your doctor if you develop a fever or pus, redness, heat, pain or tenderness near the wound, or any other signs of an SSI.

Most SSIs can be treated with antibiotics. Sometimes more surgery or procedures may be needed to treat it. During recovery, make sure that friends and family members wash their hands before and after they enter your room. Make sure all doctors and other caregivers always wash their hands, too.