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If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.
Let’s face it—pus is gross. It’s the thick, whitish goop that you see in acne, as well as other conditions. But what is it really, and why do we form pus?
Pus is a sign that your body’s immune system is working to fight off an infection. It contains white blood cells (like neutrophils), microorganisms (like bacteria), and dead tissue (Birkhauser, 2019). When your immune system detects a bacterial infection, it sends white blood cells to the infected area. Those white blood cells attack the invading microorganism, and the resulting debris is a collection of pus.
The medical terms for pus are purulent exudate, purulent drainage, and liquor puris. Most of the time, pus is white, but it can also be yellow, green, red, and brown. It’s also sometimes foul-smelling.
Since pus is an immune response, you may also experience other inflammatory symptoms in the infected areas that have collections of pus, including (CDC, 2020):
Where does pus form?
Most people are familiar with pus from skin infections. It can be near the surface—like acne (pimples or pustules) and infected hair follicles (folliculitis)—or it can be deeper—as in the case of skin abscesses (boils or furuncles). Sometimes, these furuncles cluster to form something called a carbuncle (Dhar, 2019).
Skin infections can also occur at the skin incision site after surgery, a condition called surgical-site infection (SSI) (Berríos-Torres, 2017). Some people form multiple painful abscesses, particularly in their armpits or groin, characteristic of a condition called hidradenitis suppurativa (AAD, n.d.).
However, the skin is not the only place where your body can form pus. You can also have pus develop in your mouth at the root of an infected tooth, around your tonsils (strep throat infection), or in your urinary tract. More serious purulent infections may involve other organs like your lungs (empyema), spinal cord, intestines, or brain. You can even have pus develop in your eye, within a joint, or other parts of the body—it all depends on the location of the infection.
What causes pus?
Pus forms in response to an infection, usually with bacteria. In skin infections, the culprit is usually microorganisms that live on the skin, like Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), and Streptococcus pyogenes. Just having these germs on your skin doesn’t hurt you, but if they get into the skin through a cut or along a hair follicle, they can lead to an infection and pus formation (Baiu, 2018).
Several risk factors make you more likely to develop an infection with pus formation, including (Ibler, 2014):
- Skin wound from surgery or injury/trauma
- Skin conditions, like eczema, atopic dermatitis, or athlete’s foot
- Long-standing swelling of arms or legs
- Immune system problems
How to treat pus
You can prevent skin infections by washing your hands before touching any skin wounds.
Treating pus will depend on the size and location of the infection. In the case of acne, gently cleansing your face and using acne treatments will help. You can treat small collections of pus with warm compresses to encourage the pus to drain on its own. But don’t try to “pop” areas with pus—this increases your chance of worsening infection and scarring.
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Larger collections of pus (abscesses) may need to be treated with antibiotics or drained by a healthcare provider (Spelman, 2020). In some cases, drainage can be done with a needle (a procedure called needle aspiration). In others, surgery may be necessary (a procedure called incision and drainage).
When to seek medical attention
If you notice any of the following, seek medical advice right away:
- The area around the pus is red, tender, and warm to touch—you may be developing cellulitis, an infection of the skin that can spread if not treated promptly.
- Any worsening of the pus or associated symptoms
- You develop a fever—this can signify that the infection is deeper and may even be getting into your bloodstream. This can lead to a potentially life-threatening condition called sepsis.
- American Academy of Dermatology (n.d.). Hidradenitis suppurativa: overview. Retrieved on Jan 20, 2021 from https://www.aad.org/public/diseases/a-z/hidradenitis-suppurativa-overview
- Baiu I, Melendez E. (2018). Skin abscess. JAMA;319(13):1405. Retrieved from https://jamanetwork.com/journals/jama/fullarticle/2677448
- Berríos-Torres SI, Umscheid CA, Bratzler DW, et al. (2017). Centers for Disease Control and Prevention Guideline for the prevention of surgical site infection. JAMA Surgery;152(8):784–791. Retrieved from https://jamanetwork.com/journals/jamasurgery/fullarticle/2623725
- Birkhauser, J., MD. (2018). Pus. Magill’s Medical Guide (Online Edition). Retrieved from https://www.salempress.com/Magills-Medical-Guide
- Centers for Disease Control and Prevention (CDC). (2020). Skin infections. Retrieved on Jan 20, 2021 from https://www.cdc.gov/antibiotic-use/community/for-patients/common-illnesses/skin-infections.html
- Dhar, A.D. (2019). Furuncles and carbuncles. Merck Manual Professional Version. Retrieved on Jan 20, 2021 from https://www.merckmanuals.com/professional/dermatologic-disorders/bacterial-skin-infections/furuncles-and-carbuncles
- Ibler, K. S., & Kromann, C. B. (2014). Recurrent furunculosis – challenges and management: a review. Clinical, Cosmetic and Investigational Dermatology, 7, 59–64. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934592/
- Spelman, D. and Baddour, L.M. (2020) UpToDate – Cellulitis and skin abscess in adults: treatment. Retrieved on Jan 20, 2021 from https://www.uptodate.com/contents/cellulitis-and-skin-abscess-in-adults-treatment
Dr. Mike is a licensed physician and the Director, Medical Content & Education at Ro.