Folliculitis Workup

Updated: Oct 08, 2020
  • Author: Elizabeth K Satter, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Laboratory Studies

Laboratory studies are typically not obtained because diagnosis is usually made based on history and physical examination findings alone. In cases resistant to standard therapy, cultures, Gram stain, potassium chloride (KOH) preparation, and biopsy are the diagnostic tests of choice.

Gram stain and bacterial culture are best performed by unroofing an entire pustule with a No. 15 blade and depositing material onto a glass slide and a sterile cotton swab. In typical cases, Gram stain shows gram-positive cocci, and culture grows S aureus. Pseudomonas species can be cultured from the pustules of hot tub folliculitis.

Nasal culture of family members to look for S aureus colonization may be needed in chronic cases.

KOH inspection, fungal culture, or both can be useful for diagnosing dermatophyte infections. Pityrosporum yeast forms are best appreciated on biopsy specimens in cases of Malassezia (Pityrosporum) folliculitis.

Viral culture or biopsy assists in the identification of folliculitis caused by herpes simplex virus.

A small punch biopsy (3-4 mm) of an active lesion should be performed in atypical cases or in patients resistant to standard treatments.

A complete blood cell count often reveals leukocytosis and eosinophilia, with elevated immunoglobulin E levels in patients with eosinophilic folliculitis.



For deep infections, incision and drainage can be therapeutic and can provide material to be sent for culture.


Histologic Findings

Histologically, all cases of superficial folliculitis have a similar appearance in that they show a moderately intense infiltrate of inflammatory cells in the follicular ostium and upper regions of the follicle. In most cases, the inflammation initially consists of neutrophils and then becomes more mixed with the addition of lymphocytes and macrophages. If the folliculitis is from an infectious cause, then various organisms can be identified within the follicle. [35] Note the image below.

Superficial folliculitis with neutrophils concentr Superficial folliculitis with neutrophils concentrated in the upper aspect of the follicle

Folliculitis can also extend deeper, with the inflammation involving the entire length of the follicle and often encompassing the adjacent dermis as a focal dermal abscess.

In perifolliculitis, the inflammation is restricted to the area immediately surrounding the follicle, as demonstrated in the image below.

Perifolliculitis, showing inflammatory cells surro Perifolliculitis, showing inflammatory cells surrounding the follicle,

The histopathological evaluation of herpes folliculitis can be subtle and nonspecific and often requires that deeper histological sections are obtained in order to see the characteristic histological changes. Typically, a dense lymphohistiocytic infiltrate is noted, often admixed with neutrophils that surround and frequently destroy the hair follicle. The characteristic changes of a herpes infection, namely balloon degeneration of the keratinocytes of the follicle, scattered multinucleated cells, and keratinocytes with enlarged gray nuclei that have peripheral margination of the chromatin, are seen in approximately half the cases on which a biopsy has been performed. Most cases of herpes folliculitis have been shown to be caused by a varicella-zoster infection, and, initially, the infection is centered on the sebaceous gland. [19]

In pseudofolliculitis barbae and acne keloidalis nuchae, the inflammatory infiltrate is initially perifollicular and is composed of neutrophils and lymphocytes; however, later, the predominant cells are monocytes and plasma cells. Often, free hair shafts without the accompanying follicle can be identified within the dermis. The hair shafts are typically surrounded by acute or granulomatous inflammation and fibrosis. Hypertrophic scar is often present. [35]

The light microscopic features of eosinophilic folliculitis include perifollicular infiltrates of lymphocytes and eosinophils associated with follicular eosinophilic spongiosis. This type of folliculitis is often associated with follicular mucinosis. [13]

The histological features of a papulopustular eruption due to epidermal growth factor receptor inhibitors is that of a superficial purulent folliculitis, which, in most cases, is sterile but can occasionally be associated with S aureus infection. [8]