Folliculitis, furuncles, and carbuncles: Clinical sciences

Folliculitis is a common skin condition where a hair follicle becomes infected and forms a papule or pustule over the hair-bearing skin. The infection is most commonly bacterial, but in rare cases, it can be fungal, viral, or parasitic. As the infection brews, it can form a furuncle which is an abscess involving the hair follicle and its surrounding tissue. When there are multiple furuncles, they can grow and connect subcutaneously forming a carbuncle. The diagnosis of folliculitis, furuncle, or carbuncle is clinical, so performing a thorough history and physical examination is very important.

When a patient presents with chief concern suggesting folliculitis, a furuncle, or a carbuncle, the first step is to obtain a focused history and physical in addition to labs such as a CBC. Patients typically report skin redness, pain, pruritus over a skin bump, and sometimes even fever. They might also report recent or frequent waxing or hair removal over the affected area, or that they had a pimple they tried to pop. Finally, patients might have a history of uncontrolled diabetes.

When it comes to the physical exam, it typically reveals erythema, swelling, tenderness, and possibly induration surrounding a folliculocentric papule, pustule, or nodule within the hair-bearing skin. You might also see a focal area of fluctuance with or without purulent drainage. Lastly, CBC is often normal or may show mild leukocytosis. If your patient presents with these clinical findings, suspect folliculitis, furuncle, or carbuncle.

Alright, let’s start with folliculitis, which is usually limited to the superficial dermis. On further examination, you can expect to find superficially inflamed papule around a hair follicle without any areas of fluctuance. This is very characteristic of folliculitis, so that’s your diagnosis. Once you have made the diagnosis, your next step is to treat with topical antibiotics and advise cessation of hair removal. Then, assess the response between 48 to 72 hours of starting treatment.

If there is an adequate response with improvement or resolution of redness, inflammation, and pain, the patient can complete the course of antibiotics. However, if there is an inadequate response, meaning no change in clinical status or the condition has worsened, start empiric oral antibiotics and assess for a spreading infection or formation of an abscess.

If the condition does not improve with continuing treatment, assess for unlikely microorganisms like fungal, viral, or parasitic infection. Obtaining a culture might be helpful to identify the organism and tailor your treatment accordingly.

Here is a high-yield fact! Bacterial folliculitis is most commonly caused by Staphylococcus aureus, which is part of the skin flora. In some cases, gram-negative organisms like Pseudomonas aeruginosa can cause what is known as “hot tub” folliculitis. Infections with less common bacteria like Klebsiella and Enterobacter are associated with folliculitis that arises after long-term oral antibiotic therapy.