What Is Pus?

Pus is a thick fluid matter produced as part of the body's inflammatory response to an infection. It consists of a buildup of degenerating white blood cells, dead or living bacteria (or other microorganisms), and tissue debris. Pus is typically an opaque white-yellow color but can be tinted brown or even green. It's usually odorless although certain types of bacteria produce foul-smelling pus.

The medical term for pus is purulent exudate. It is also sometimes called purulent drainage, and the fluid is sometimes referred to as liquor puris.

A small amount of pus, such as from pimples, typically isn't a cause for alarm, but pus at the site of a wound, surgical incision, or deep interior location may require medical intervention. Treatments for infections with pus may include antibiotic medications, drainage procedures, or surgical removal of infected tissues.

Function

Pus is an indication your body has started to combat infection by sending infection-fighting cells to the area.

Pus is often part of an abscess, a collection of pus in a cavity formed from the breakdown of infected tissues. Abscesses can happen just under the skin or anywhere in the body and typically are the result of bacteria such as Streptococcus or Staphylococcus aureus  gaining access to tissues, such as through a small opening in the skin.

Fungus or parasites can also lead to abscesses. Once the bacteria or other microorganism starts multiplying, they release toxins that destroy cells. This triggers an immune response in which leukocytes (white blood cells) head to the site to kill and absorb the bacteria and break down the dead tissue. During this process, white blood cells also break down and die, forming the pus.

Types

Pus can be visible on the surface of the skin or it may form internally as a complication of an infection or injury.

Skin Infection

Types of skin conditions characterized by pus on or just beneath the skin's surface include:

• Acne: Pores clogged with oil and debris form pimples or pustules on the skin's surface that contain pus.
• Folliculitis: Small acne-like bumps from infected hair follicles
• Boils or furuncles: Painful nodular bumps from infected hair follicles that are typically caused by Staphylococcus aureus
• Carbuncles: A group of connected boils
• Superficial surgical site infection (SSI): An SSI is at the skin level only, where pus can form along the incision, which may become red and painful when touched.
• Trauma wounds: Pus and yellow crust at the site of a wound caused by injury or physical trauma may be accompanied by pain or swelling.

Internal Infection

Pus-filled abscesses can form internally, such as in the mouth or alongside internal organs. It can be a result of a surgical complication, injury, or untreated bacterial or fungal infection. There are many types of internal abscesses and conditions that can lead to pus, including:

• Abscessed tooth: A dental infection in or near the root of a tooth
• Deep SSI: An infection can occur internally in muscles and other tissues or may form in the organ or area of the surgery
• Peritonsillar abscess: Spots of pus at the back of the throat or behind the tonsils can form as a symptom of strep throat or tonsillitis
• Empyema: A collection of pus in the pleural space between the lungs and the chest wall that can be a complication of bacterial pneumonia or lung surgery
• Brain abscess: A rare swelling of pus in the brain that can be caused by a bacterial or fungal infection
• Septic arthritis: A serious joint infection that can form after bacteria travels through the bloodstream to the joint

Causes

Punctures, scrapes, scratches, or other openings in the skin can allow bacteria that live on the skin to enter the body and cause an infection. This includes surgical incisions. There can also be deep internal infections with pus that occur after surgery, injuries, or illnesses.

There are certain factors and underlying conditions that can put you at risk for infections and wound complications with pus:

• Poor hygiene, such as not washing your hands before touching a wound
• Diabetes
• Older age
• Smoking
• Severe obesity
• An immune system disorder, HIV infection, or cancer
• Medications that reduce immune system activity, such as corticosteroids or immunosuppressants
• Paralysis or limited mobility
• Low body temperature
• Long operations and hospitalization
• Emergency procedures

For people who have compromised immune systems, pus may never form in an infected area, but most will find that infection leads to discharge from the area as well as the possibility of redness, pain or tenderness, swelling, and fever.

Treatment

Most SSIs and skin wounds are treated with oral antibiotics or ointments. Antibiotics are important because they help the body heal faster and may prevent an infection from becoming worse.

Your physician may collect your wound drainage and send it to a lab to determine what type of bacteria is causing the infection. This process, called a culture and sensitivity test, can be used to determine which antibiotic the bacteria is sensitive to and may kill the bacteria most efficiently.

For post-surgery pus, your physician may recommend a special incision care program and may want to see your incision in order to make sure there isn’t an underlying problem.

In some cases, an abscess drainage procedure to remove pus or surgical debridement (removal of dead tissue) may be needed to address the infection.

In cases of sepsis, a dangerous and life-threatening condition in which an infection enters the bloodstream and can spread throughout the body, hospitalization will be required.

Prevention

There are simple things you can do to reduce your risk of developing an infection with pus:

• Wash cuts and other wounds gently with soap and water
• Follow your physician's care instructions after surgery or hospitalization for injuries
• Wash your hands thoroughly and regularly
• Don't squeeze pus out of pimples or boils. Instead, gently apply a warm compress several times a day
• Don't share towels or razors
• Eat a healthy, balanced diet
• Be vigilant about controlling your blood sugar control if you have diabetes
• Quit smoking

Preparing for Surgery

Between 1% and 3% of people who have surgeries develop an infection, according to the Centers for Disease Control and Prevention. There are steps you can take before and after any procedure to reduce your risk of an SSI.

Keep the incision dry and protect it with a clean bandage. You can leave it uncovered, but if drainage leaks from the site it can stain clothing and make a bigger mess than necessary. In general, do what was recommended in your instructions for incision care after surgery unless you are told otherwise.

When to Call Your Doctor

Always contact your doctor if you see pus, especially after physical trauma or surgery, or have any redness or pain with a wound since these are all signs of infection.

A surgical incision with pus should not be ignored, but many types of drainage are normal. Clear fluid or blood-tinged fluid that is largely clear, is considered normal unless there is a large quantity coming from the wound.

If you have any cloudy or white-yellow drainage, it should be promptly examined by a healthcare provider. This doesn't mean that a tiny speck of white drainage should lead to calling 911 at 2 a.m., but pus should not be ignored for days. Ignoring an infection can lead to serious problems, a longer recovery, and more scarring. Calling your physician or surgeon should be a priority.

If you have a wound or surgical incision and experience any flu-like symptoms, even without pus, seek urgent medical care. Untreated infections can put you at risk of serious or even life-threatening conditions, such as sepsis, and should not be ignored.

A Word From Verywell

One of the most important things you can do to avoid an infection with pus is to wash your hands often. This is crucial before and after caring for skin bumps, incision, or wounds. If it is too late to prevent an infection, follow guidance from your physician so you can promote healing and minimize tissue damage and complications.

If you have a wound, plan to take the time to clean it appropriately, check the wound regularly for any signs of infection, and be sure to protect it when necessary.