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Hair Follicles in Mammal Skin

Image: “Mammalian skin showing hair follicles.” by Circa24 – Own work. License: CC BY-SA 3.0

Definition of Folliculitis

Folliculitis is an inflammatory condition characterized by inflammatory cells in the wall of a hair follicle. The presentation is, therefore, a follicular pustule.

Superficial folliculitis is the restricted inflammation of the infundibular part of the follicle.

Deep folliculitis refers to inflammation of the hair follicle with dermal involvement.

Perifolliculitis is the inflammation of the surrounding dermis with little involvement of the hair follicle. Acne is considered a form of folliculitis that is not infectious-related.

Epidemiology of Folliculitis

Superficial folliculitis is a common condition that is usually mild and self-limited. The exact incidence of superficial folliculitis is unknown. Frequent shaving, patients on immunosuppression therapy, dermatosis, antibiotic use, diabetesand obesity are recognized as folliculitis risk factors. Patients taking epidermal growth factor receptor inhibitors are very likely to develop folliculitis.

Gender does not seem to affect the incidence of the condition, but the type of folliculitis seems to be correlated with the patient’s sex. While men are more likely to develop eosinophilic folliculitis, folliculitis in women is usually caused by a pityrosporum infection.

Pathophysiology of Folliculitis

The most common etiology of folliculitis is infectious-related. Bacterial, fungal, and parasitic infections are associated with folliculitis. Possible non-infectious etiologies of folliculitis include trauma, inflammation, and the use of certain drugs, such as antibiotics or epidermal growth factor inhibitors.


Image: “Folliculitis.” by Vivvid – Own Work. License: CC BY-SA 3.0

Eosinophilic folliculitis is an autoimmune condition characterized by an inflammatory response against sebocytes. The principal inflammatory cell infiltrate in these patients is eosinophils.

Almost all patients taking epidermal growth factor inhibitors are at risk of developing folliculitis. The exact mechanism of folliculitis in these patients is not fully understood, but might be related to disrupted follicular epidermal differentiation and subsequent follicular obstruction.

Clinical Presentation of Folliculitis

Folliculitis semiology differs depending on the disease stage. Patients with superficial folliculitis complain of acute pruritus around the inflamed area. On the other hand, patients with deep folliculitis may report a previous history of chronic superficial folliculitis. Patients with deep folliculitis can have pus drainage from their pustules. Additionally, they can develop scarring from previous and recurrent folliculitis eruptions.

Patients receiving epidermal growth factor inhibitors usually present with the follicular eruption within two weeks of initiating treatment. The most common sites are the face, scalp, chest, and upper back.

Physical examination of the inflamed area reveals multiple papules and pustules. The area surrounding the pustules is usually red. The pustules can have central hair piercing them. The most commonly involved sites are the face and scalp, followed by the thighs and axilla.

The most common cause of superficial folliculitis is staphylococcus aureus infection of the hair follicle. If left untreated, the pustules can rupture and form a golden crust. In a few patients, the condition can evolve into a boil, which is a dermal abscess.

Patients with tinea barbae infection develop superficial folliculitis that is confined to one side of the face. These patients are usually men who work in the agricultural industry and report having direct contact with farm animals.

Those who receive long-term antibiotics usually develop gram-negative folliculitis. The patients develop multiple lesions around the nose and on the face. The most commonly identified organisms are Enterobacter, Klebsiella, and Escherichia.

Some patients report a recent history of soaking in a tub or a swimming pool before the follicular eruption. This form of folliculitis is usually related to pseudomonas infection and resolves within two weeks.

Young females who present with back and chest follicular eruption might have Malassezia furfur infection. This fungal infection is responsible for the Pityrosporum folliculitis type. After shaving bumps are another form of folliculitis that is usually non-infectious in etiology.

Japanese men, AIDs patients, and infants tend to develop eosinophilic folliculitis. The condition presents with a pustular rash that consists of papules and pustules. Eventually, these pustules coalesce with each other and form a circinate plaque. The typical picture would be a circle with a rim of pustules and a clearing center. These lesions can be found on the face, back and arms.

Diagnostic Work-up for Folliculitis

Staphylococcus aureus gram stain

Image: “Microscopic image of Staphylococcus aureus (ATCC 25923). Gram staining, magnification: 1,000.” by Y Tambe. License: CC BY-SA 3.0

The diagnosis of folliculitis is clinically based. In resistant cases, gram stain, potassium hydroxide preparation, and biopsy are of value in determining the etiology of the condition and directing the treatment towards a more specific approach.

If a gram stain or a bacterial culture is indicated, a pus swab from the pustules should be obtained to identify gram-positive cocci. The most common isolated organism is Staphylococcus aureus.

Potassium hydroxide preparation of the pustule’s swab is indicated if the etiology is suspected to be fungal. Patients with deep folliculitis should undergo incision and drainage of their abscesses. This procedure requires confirmation of the diagnosis and is usually therapeutic.

If a biopsy is performed, the typical picture would be that of an intense inflammatory cell infiltrate into the follicular ostium. Neutrophils, lymphocytes, and macrophages are the most commonly identified inflammatory cells on biopsy. Patients with eosinophilic folliculitis have an eosinophilic cell infiltrate, as the name implies.

Patients with perifolliculitis present a similar picture to folliculitis but without direct hair follicle involvement. Instead, the inflammatory cell infiltrate is usually confined to the areas surrounding the follicle.

Treatment of Folliculitis

The treatment plan for folliculitis should be tailored to the most likely etiology. Patients with uncomplicated superficial folliculitis do not need systemic antibiotics. Antibacterial soap is usually sufficient.

In a few patients, the pustules become intensely painful. In that case, warm compresses, with or without topical antibiotics, can be helpful. Patients with deep folliculitis should receive oral antibiotics.

The most commonly used systemic antibiotic for folliculitis is dicloxacillin or a cephalosporin. Non-responders should be prescribed clindamycin, minocycline, or linezolid.

Patients with deep folliculitis should undergo an incision and drainage procedure, which can be curative.

Patients with recurrent perinasal folliculitis might benefit from mupirocin ointment to eradicate the causative organism, staphylococcus aureus.

Patients with Pseudomonas folliculitis typically improve without treatment. Eosinophilic folliculitis responds to indomethacin 50 mg/day, minocycline, or dapsone. Those who have Pityrosporum folliculitis should get a ketoconazole cream. If patients develop a relapse, systemic antifungals are indicated.

Epidermal growth factor receptor inhibitors can cause self-limited folliculitis which requires no specific treatment. Those who develop folliculitis because of receiving chronic antibiotics benefit from discontinuing the current antibiotic and receiving trimethoprim-sulfamethoxazole.

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