Is Pus a Sign of Infection? What Causes It?

Pus is a thick fluid that builds up when an injury becomes infected. But pus isn't the only sign of an infection.

The word “pus” conjures all kinds of unpleasant images. It’s linked with injuries and infection and no one likes to think about that.

Pus is a thick fluid that builds up when an injury becomes infected. It can be white, yellow, green, or brown. It may have a foul odor but that is not always the case. It may have no scent at all.

But pus is a natural part of the healing process for wounds. Pus is a sign that a wound is infected but it is also a sign that your body is trying to fight the infection and heal the injury.

Once an infection has started, your immune system begins trying to fight it off. It sends white blood cells to the area to destroy the bacteria. The white blood cells wear out and die after a while, as does some of the injured tissue. The residue collects in the injured area and becomes what we call pus.

Learn more about pus, why it appears, and how to treat an infected wound.

Pus isn’t the only symptom of an infection. The area will usually look red and swollen. It may be warm to the touch and the infected spot could be painful. If the situation gets worse, you might notice symptoms like fever, aches, or chills as your body fights the infection.

Pus often shows up in an abscess, a space that develops when there is a breakdown in your body’s tissue. When the outer layers of skin break for any reason, bacteria can enter the wounds and cause an infection. Abscesses can occur on the body, including the skin, mucus membranes, or your internal organ.

Skin abscesses are very common. Anything from a small cut to an ingrown hair can be a point of entry for bacteria. Sometimes these small wounds get infected and come to a head, similar to a pimple. There will be a pocket of pus visible on top of a red, painful bump.

Eventually, the abscess will rupture and drain, which helps the healing process.

Infections can also happen below the skin. When that happens, you may notice a swollen, red area that is painful to the touch. You can’t see it, but pus is collecting in the abscess. If you don’t get treatment, the infection can worsen or spread.

Surgical wounds are also at risk for infections. You may notice new or worsening pain around the incision if it gets infected. Swelling and redness are signs of infection, along with any pus that soaks through bandages or comes out in a drainage tube.

If the infection is small — less than half an inch across — you can probably treat it at home with warm compresses.

You should see a doctor if you have a sore that is larger than half an inch. Also, call the doctor if a small wound gets bigger or more painful or if you have a fever. You should also see a doctor if the area develops red streaks, which might mean the infection is spreading.

Any infection in the groin area or near your anus needs medical attention as well.

For surgical site infections, you should call the doctor who did your operation. Call a dentist if you have an abscess under a tooth.

When you see your doctor, they will want to know how the injury happened and how long you have had the infection. They will examine the wound and the surrounding area to get an idea of how large the infection might be.

Your doctor might also collect some of the pus from the infection and test it for bacteria or fungus. The test results will help them prescribe medication to clear up the infection.

Pus-filled abscesses often need to be drained in order to heal completely. Your doctor will decide how to do that based on where the abscess is on your body. It could be something the doctor can do in the office or you might need a more extensive procedure.

Your doctor will use a local anesthetic to numb the area, then drain the pus. They might use a needle to draw it out. They might also make an incision and drain it through that opening.

Dental abscesses can be treated in the office. Your dentist will numb the area and clean out the infection. You will probably need a root canal to solve the problem.

After the pus is cleaned out of the wound, your doctor may give you antibiotics to prevent it from coming back. You should take any medication as directed. You should also follow all the instructions your doctor gives you about caring for the wound when you get home.