Trust us—you don't want to see the "before" photograph. The bandage is covering an unsightly batch of pus—a sign of infection that's being fought off by your immune system.

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You had a fall and suffered the tell-tale scrape on your knee. Within a week, it’s filled in with green pus. Don’t worry, there’s no alien at play here. Pus is a sign that your body’s defense system has kicked in. All you need to do is figure out what caused the infection your immune system is trying to fight—and learn how to treat it.

What is Pus? | Treatment | Pus Color Chart

First, let’s learn a bit more about what pus is. Yes, it’s gross. Yes, it can be smelly. And yes, it’s a sign of infection. But what is it made of? And what is a pus infection?

What Is Pus?

Pus is a thick, opaque, often whitish-yellow or brownish-yellow fluid that’s formed during an inflammatory response (i.e., in reaction to an infection). It’s made up of dead white blood cells (a.k.a. macrophages and neutrophils), bacteria, and other tissue debris produced during the body’s immune response to the infection. It can also be a fungal or viral reaction.

In other words, pus is a natural byproduct of your body’s healing process. It’s akin to an error message on your computer, alerting you to the fact that there’s a bug in your system.

Remember your old friend, the pimple? Pimples form when pus gathers near or on the skin’s surface. Same goes for a pustule. An abscess is created when pus builds up in an enclosed area of tissue.

Pus can appear anywhere—on your tonsils, face, inside a joint, on the brain, or in the gastrointestinal tract, for instance.

How Do You Treat a Pus Infection?

The key to getting rid of it is to “treat the underlying infection,” says Rebecca Baxt, MD, a New Jersey-based dermatologist. Treatment will depend on the type of infection you’re fighting.

According to Dr. Baxt, the most common methods for treating pus infections include:

• Antiviral medications
• Antifungal medications
• Creating an incision in and then draining the infected area
• Oral antibiotics
• Topical anti-infection solutions

Treatment for a Pus Infection

To treat a minor pus infection—a pimple or very small skin abscess, for example—at home, try this: Apply a clean, warm towel to the pus infection. Hold for five minutes to reduce swelling and open the skin to help speed healing and encourage drainage.

(To learn more about treating an infected wound, read our post 11 Signs of an Infected Wound: Stop the Ooze Before It Starts.)

For a minor abscess, try this:

• Clean the infection with soap and water
• Rinse and pat dry with a clean towel
• Clean the abscess again with peroxide
• Remove any debris or pus with clean hands
• Apply a topical antibiotic (e.g. Neosporin) to the infected area
• Cover the area with a clean, soft gauze
• Seek medical help if your condition worsens

When to See the Doctor for Pus Infected Wound

A bigger buildup of pus, especially one that’s not easily accessible (e.g., in the mouth or under the armpit), may require a doctor or surgeon’s help. He or she will likely make an incision and drain the infected area.

Below are a few examples of doctor-worthy infections:

• Large or hard-to-reach abscesses. These may need to be surgically opened to drain it.
• Recurring ear inflammation or infections. Grommets, or small plastic tubes, may need to be inserted in the ear to aid drainage.
• Septic arthritis. A surgeon may need to drain the joint to remove infected pus before administering antibiotics.

If you have a new wound, you may need to get stitches. 

Note: If you’re noticing pus after a recent surgery, contact your doctor immediately. Do not apply antibiotic cream, alcohol or peroxide to the area. Also, seek medical help if you experience other signs of an infection, including:

• A high fever
• Swelling
• Redness around the wound
• Warmth around the wound
• Confusion
• Severe pain
• Headache
• Trouble breathing
• Loss of consciousness

What Does Pus Look Like? 

There are many different colors of pus, including whitish, yellow, green, or brown. The color is caused by the accumulation of dead neutrophils (i.e. white blood cells). In some cases, pus is accompanied by a foul smell.

According to Dr. Baxt, the colors of a pus infection could indicate what type of illness you’re suffering from. Here are a few examples of the illness related to the color of pus:

This article was originally published in 2018. It is regularly updated.