Practice Essentials
Malassezia (Pityrosporum) folliculitis (MF) is an inflammatory skin disorder that typically manifests as a pruritic, follicular papulopustular eruption distributed on the upper trunk of young to middle-aged adults. Pityrosporum folliculitis was first described by Weary et al in 1969, and it was identified as a separate clinical and histologic diagnosis by Potter et al in 1973.
Yeasts, Malassezia furfur in particular, are the pathogens in MF. M furfur has been linked to several skin diseases, including seborrheic dermatitis, folliculitis, confluent and reticulated papillomatosis, and pityriasis versicolor. [1, 2, 3] In 1874, Malassez described round and oval budding yeasts from scales of patients with seborrheic dermatitis, using the phrases "bottle bacillus of Unna" for the small oval cells in the scale and "spore of Malassez" for the bud associated with the yeast. In 1904, Saborouraud proposed the genus Pityrosporum for the budding yeast cells without hyphal elements from normal skin. Later in the 1900s, the species Pityrosporum ovale and Pityrosporum orbiculare were isolated.
As a consequence of controversy and confusion regarding the grouping of various lipophilic yeasts and fungi of the skin, these two yeast species, collectively with fungal forms, were reclassified under a single name, M furfur, which applies regardless of the morphology of the organism. Subsequent advances in technology led to the recognition of seven species of Malassezia: M furfur, Malassezia pachydermatis, Malassezia sympodialis, Malassezia globosa, Malassezia obtusa, Malassezia restricta, and Malassezia slooffiae. [4] Additional species have since been identified. [1]
MF is caused by Malassezia species that are part of the cutaneous microflora and not by exogenous species. [5] However, the focus of this article is M furfur, which is considered the primary pathologic agent of MF. Lesions are chronic, erythematous, pruritic papules and pustules, which occur in a follicular pattern. These lesions are usually present on the back and chest and, occasionally, on the neck, shoulders, upper arms, and face.
The diagnosis of MF is based on clinical suspicion of the classic presentation of pruritic papulopustules found in a follicular pattern on the back, the chest, the upper arms, and occasionally the neck. They are rarely present on the face. An improvement in the lesions with empiric antimycotic therapy supports a clinical diagnosis of MF. (See Presentation and Workup.)
Both topical and oral antifungals are effective therapeutic agents for this condition. Although many patients improve with topical azole medications, some cases require oral therapy. Patients have been successfully treated with oral pulse itraconazole and weekly fluconazole. M sympodialis is highly sensitive to terbinafine, whereas other species are more resistant to it. Oral ketoconazole is no longer recommended. Oral medication should be discontinued when the lesions resolve. (See Treatment.)
In 2023, the European Academy of Dermatology and Venereology (EADV) published a position statement containing recommendations for the diagnosis and treatment of MF. [6] (See Guidelines.)
Pathophysiology
M furfur (ie, P ovale and P orbiculare) is a lipophilic, saprophytic, budding, unipolar, dimorphic, gram-positive, double-walled, oval-to-round yeast. Malassezia yeasts are classified as superficial mycoses that by definition do not invade past the cornified epithelium. In MF, however, the organisms are present in the ostium and central and deep segments of the hair follicle.
MF is believed to result from plugging of the follicle followed by an overgrowth of yeast that thrives in the sebaceous environment. Malassezia yeasts require free fatty acids for survival. Usually, they are found in the stratum corneum and in pilar folliculi in areas with increased sebaceous gland activity such as the chest and back. The yeasts hydrolyze triglycerides into free fatty acids and create long-chain and medium-chain fatty acids from free fatty acids. The result is a cell-mediated response and activation of the alternative complement pathway, which leads to inflammation.
Etiology
MF is caused by Malassezia yeasts, which are lipophilic. Several factors can lead to changes in immunity, sebum production, and the growth of skin flora. These factors help to produce favorable conditions for growth of these yeasts.
Systemic diseases and pharmacologic agents that encourage the growth of yeast, possibly because of alterations in immunity, include the following:
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Diabetes mellitus
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Cushing disease
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Hodgkin disease [7]
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Cancer treated with cetuximab, a chimeric (mouse/human) monoclonal antibody epidermal growth factor receptor (EGFR) inhibitor for the treatment of metastatic colorectal cancer and head and neck cancer [8]
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HIV infection
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Crohn disease treated with infliximab, a monoclonal antibody against tumor necrosis factor (TNF)-α [12]
An increase in sebum production, such as that in pregnancy, [13, 14] and high levels of androgens may potentiate the development of MF.
Antibiotics can alter normal skin flora, allowing the yeast to proliferate.
MF occurs more frequently in environments of high heat and humidity.
Occlusion of the skin and hair follicles with cosmetics, lotions, sunscreens, emollients, olive oil, or clothing creates favorable conditions for MF.
Anticonvulsant therapy and Down syndrome [15] are other conditions that are associated with MF.
Other related and coexisting conditions may include the following:
Some individuals seem to have an innate propensity for MF. In one experiment, Malassezia yeasts were applied to occluded forearm skin in patients with MF. Flares of folliculitis occurred at the application site. In the same experiment, MF did not develop in patients with no prior diagnosis of the condition.
Epidemiology
United States and international statistics
Malassezia organisms can be found on the skin in 75-98% of healthy people in the United States. These organisms are part of the normal skin flora of many individuals who do not have signs or symptoms of folliculitis or other disease. Colonization by M furfur begins soon after birth, and the peak presence of the yeasts occurs in late adolescence and early adult life, coinciding with increasing activity of sebaceous glands and concentration of lipids in the skin.
Worldwide, P ovale has been found to be present on 90-100% of the surface of healthy skin, with higher numbers noted on the chest and back. Certain climates influence the percentage of people with this organism and the number of people with MF. People living in warm and humid climates have a higher incidence of MF. One clinic in the Philippines documented that 16% of all patient visits were a result of this condition. [17] A 2008 report from China found that 1.5% of all dermatology patients were diagnosed with MF, most of them healthy middle-aged males. [18]
Age-, sex-, and race-related demographics
MF is recognized as a condition that affects youths and young and middle-aged adults, [19] most commonly between the ages of 13 and 45 years. However, Archer-Dubon et al reported three cases that occurred in an intensive care unit (ICU) setting in older individuals who were in consecutive beds, who received care from the same nursing staff, and who all received high-dose antibiotics. [20] Very young individuals can also be affected. [3]
Reports of the relative frequency of MF in males and females have varied, ranging from a male-to-female ratio of 1:1 to a predominance of one sex or the other. Literature from the past decade has suggested that the female-to-male ratio might be a little higher. [21]
No racial differences in the frequency of MF are known to exist.
Prognosis
The prognosis is good. With treatment, MF can completely resolve; without treatment, MF lesions are classically pruritic. Although MF may be quite bothersome (as a result of severe pruritus), the lesions are benign.
Among the underlying conditions that predispose the patient to MF are diabetes mellitus, immunodeficiency, and systemic candidiasis [22] ; these conditions may cause morbidity. The presence of such predisposing conditions should be taken into account when MF is diagnosed.
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This photo is high-power hematoxylin and eosin staining of a biopsy confirming Pityrosporum folliculitis. There is a hair shaft within a hair follicle with scattered amphophilic staining circular Pityrosporum yeast. Courtesy of Ronald Rapini, MD.
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Left: A 25-year-old man with complaints of slightly pruritic, monomorphic follicular papules, pustules, and secondary keloid on the upper trunk and neck. Right: Scanning electron microscopy of the hair follicle from the upper trunk. This demonstrated a large number of globular or orbicular-ovate yeasts of budding daughter cell, with collar structure around the budding. Courtesy of Wikimedia Commons by Ran Yuping et al (https://commons.wikimedia.org/wiki/File:Pityrosporum_folliculitis_2.jpg).
