What Is a Carbuncle?

Learn more about this collection of infected hair follicles

A carbuncle is a collection of multiple infected hair follicles. It is an abscess, just like a furuncle, but a carbuncle is a much more serious infection. The key difference: A furuncle is an infection of a single hair follicle and its surrounding tissue, while a carbuncle is actually several furuncles that are densely packed together.

Risk Factors

Some factors put you at elevated risk for developing carbuncles.

These include: having a compromised immune system, having diabetes, having skin conditions such as acne or eczema, and having close contact with a person who has a staph infection. 

What Does a Carbuncle Look Like?

A carbuncle usually extends into the deeper layers of the skin—the subcutaneous fat. It forms into a broad, red, hot, painful nodule that often drains pus through multiple openings of the skin. Someone who has a carbuncle likely will feel sick and have a fever and fatigue. Carbuncles tend to occur in areas with thicker skin like the nape of the neck, the back, or the thighs.

How It's Diagnosed

If you think that you may have a carbuncle, call your primary care provider or a dermatologist (a doctor who specializes in treating the skin). Carbuncles are diagnosed based on their typical appearance, but sometimes they can be confused with a ruptured epidermoid cyst. There aren't any tests that are performed to decide whether an infection is a carbuncle, but often the pus inside the carbuncle is tested with a gram stain or bacterial culture to determine whether the bacterium causing the infection is a typical Staphylococcus aureus (a.k.a. staph) strain or one that is resistant to the usual penicillin-type antibiotics (like MRSA, see below for more details).

Common Treatment 

Because carbuncles usually contain a significant amount of pus, they are often first treated with a procedure called incision and drainage (I&D). This drains the pus and allows the infection to heal from the inside out. (It's best not to try to do this yourself at home by pricking it or squeezing it, because you may end up making it worse and spreading the infection.)

Since carbuncles are typically caused by the bacterium Staphylococcus aureus, the usual medications that are used to treat staph infections include the antibiotics dicloxacillin or cephalexin. 

Unfortunately, there is a somewhat new strain of staph that is resistant to these types of antibiotics. For more on that, keep reading.

Once the carbuncle has healed, there may be a scar. 

Carbuncles Caused by MRSA

Over the past several years, there has been a sharp increase in the incidence of infections caused by a special strain of Staphylococcus aureus that is resistant to the normal penicillin-based antibiotic treatment. Until recently, MRSA (short for methicillin-resistant Staphylococcus aureus) was an uncommon bacterial strain that occurred in nursing homes and other long-term care facilities. But with the overuse of antibiotics for conditions that don't require antibiotics, MRSA infections are now, unfortunately, common in certain regions of the United States.

These infections often occur spontaneously in the groin, buttock, and upper thigh region. Currently, there are antibiotics that do treat this resistant strain. The antibiotic of choice for MRSA infections that were not acquired from a hospital or long-term care facility is trimethoprim-sulfamethoxazole (a.k.a. Septra or Bactrim).

The next option is clindamycin, especially for people who are allergic to sulfa.

Sources:

Halpern, Analisa, and Warren Heymann. "Bacterial Diseases." Dermatology. 2nd. Ed. Jean Bolognia. New York: Mosby, 2008: 1075-84.

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