A young girl is seen for multiple papules and pustules on her lower abdomen (Figure 100-1). Further questioning demonstrates that she was in a friend’s hot tub twice over the previous weekend. The outbreak started after she went into the hot tub the second time. This is a case of Pseudomonas folliculitis or “hot tub” folliculitis. The patient avoided this hot tub and the folliculitis disappeared spontaneously.

Folliculitis is an inflammation of hair follicles usually from an infectious etiology. Multiple species of bacteria have been implicated, as well as fungal organisms.

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  Folliculitis is a cutaneous disorder that affects all age groups and races, and both genders.

  
  
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  It can be infectious or noninfectious. It is most commonly of bacterial origin (Figure 100-2).

  
  
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  Pseudofolliculitis barbae is most frequently seen in men of color and made worse by shaving (Figure 100-3).¹ It is also known as “razor bumps” and can start in the teen years with the onset of shaving.

  
  
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  Acne keloidalis nuchae or keloidal folliculitis is commonly seen in black patients, but can be seen in patients of any ethnic background (Figures 100-4 and 100-5).² Like pseudofolliculitis barbae, it is exacerbated by shaving.

  
  
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  Methicillin-resistant Staphylococcus aureus (MRSA) can pose a challenge to the treatment of folliculitis (Figure 100-6).

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  Folliculitis is an infection of the hair follicle and can be superficial, in which it is confined to the upper hair follicle, or deep, in which inflammation spans the entire depth of the follicle.

  
  
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  Infection can be of bacterial, viral, or fungal origin. S. aureus is by far the most common bacterial causative agent.

  
  
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  The noninfectious form of folliculitis is often seen in adolescents and young adults who wear tight-fitting clothes. Folliculitis can also be caused by chemical irritants or physical injury.

  
  
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  Topical steroid use, ointments, lotions, or makeup can swell the opening to the pilosebaceous unit and cause folliculitis.

  
  
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  Bacterial folliculitis or Staphylococcus folliculitis typically presents as infected pustules most prominent on the face, buttocks, trunk, or extremities. It can progress to a deeper infection with the development of furuncles or boils (Figure 100-7). Infection can occur as a result of mechanical injury or via local spread from nearby infected wounds. An area of desquamation is frequently seen surrounding infected pustules in S. aureus folliculitis.^1–3

  
  
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  Parasitic folliculitis usually occurs as a result of mite infestation (Demodex). These are usually seen on the face, nose, and back and typically cause an eosinophilic pustular-like folliculitis.¹

  
  
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  Folliculitis decalvans is a chronic form of folliculitis involving the scalp, leading to hair loss or alopecia (Figure 100-8). Staphylococci infection is the usual causative agent, but there also has been a suggested genetic component to this condition.¹ It is also called tufted folliculitis because some of the hair follicles will have many hairs growing from them simultaneously (Figure 100-9).

  
  
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  Acne keloidalis nuchae is a chronic form of folliculitis found on the posterior neck that can be extensive and lead to keloidal tissue and alopecia (Figures 100-4 and 100-5).^1–3

  
  
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  Fungal folliculitis is epidermal fungal infections that are seen frequently. Tinea capitis infections are a form of dermatophytic folliculitis (see Chapter 122, Tinea Capitis). Pityrosporum folliculitis is caused by yeast infection (Malassezia species) and is seen in a similar distribution as bacterial folliculitis on the back, chest, and shoulders (Figure 100-10; see Chapter 126, Tinea Versicolor). Candidal infection is less common and is usually seen in individuals who are immunosuppressed, present in hairy areas that are moist, and unlike most cases of folliculitis, may present with systemic signs and symptoms.^1–4

  
  
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  Pseudomonas folliculitis or “hot tub” folliculitis is usually a self-limited infection that follows exposure to water or objects that are contaminated with Pseudomonas aeruginosa (Figure 100-1). This occurs when hot tubs are inadequately chlorinated or brominated. This also occurs when loofah sponges or other items used for bathing become a host for pseudomonal growth. Onset of symptoms is usually within 6 to 72 hours after exposure, with the complete resolution of symptoms in a couple of days, provided that the individual avoids further exposure.⁴

  
  
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  Gram-negative folliculitis is an infection with Gram-negative bacteria that most typically occurs in individuals who have been on long-term antibiotic therapy, usually those taking oral antibiotics for acne. The most frequently encountered infective agents include Klebsiella, Escherichia coli, Enterobacter, and Proteus.⁵

  
  
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  Pseudofolliculitis barbae (razor bumps) is most commonly seen in black males who shave. Papules develop when the sharp edge of the hair shaft reenters the skin (ingrown hairs), and is seen on the cheeks and neck as a result of curled ingrown hair.² It can also occur in females with hirsutism who shave or pluck their hairs.

  
  
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  Viral folliculitis is primarily caused by herpes simplex virus and molluscum contagiosum.⁴ Herpetic folliculitis is seen primarily in individuals with a history of herpes simplex infections type I or II. But most notably, it may be a sign of immunosuppression, as is the case with HIV infection.⁶ The expression of herpes folliculitis in HIV infection ranges from simple to necrotizing folliculitis and ulcerative lesions. Molluscum is a pox virus and molluscum contagiosum has been well-documented in similar patient populations (i.e., HIV and AIDS) and in children (see Chapters 114, Herpes Simplex and 115, Molluscum Contagiosum).^6–7

  
  
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  Actinic superficial folliculitis is a sterile form of folliculitis seen predominantly in warm climates or during hot or summer months. Pustules occur primarily on the neck, over the shoulders, upper trunk, and upper arms, usually within 6 to 36 hours after sun exposure.⁸