Malassezia, a commensal fungus, constitutes normal skin microbiota. However, it may become a pathogenic yeast in multiple associated dermatological disorders and various clinical manifestations in certain conditions and individuals. A unique host-agent interaction that triggers the production of several virulence factors, such as extracellular lipase; indoles; reactive oxygen species; lipooxygenase; azelaic acid; melanin; hyphae formation; cell surface hydrophobicity, adherence and immune response stimulation; biofilm formation; influences this phenomenon. 

In a recent review, Kurniadi et al have discussed Malassezia virulence factors that contribute to the transformation of Malassezia from commensal to pathogenic and their role in dermatological disorders, including pityriasis versicolor, seborrheic dermatitis, Malassezia folliculitis, atopic dermatitis and psoriasis.

In the skin, Malassezia yeasts acquire nutrient and sebum lipids to form their outer surface and amino acids to synthesize melanin and aryl hydrocarbon receptor (AhR) indolic ligand. Further, they can also modify the excretion of lipase and phospholipase under the influence of β-endorphin. Cellular components induce the host innate and adaptive immune system. AhR ligand tends to down-regulate the immune response, modify epidermal cell function, interfere with AhR-UV-induced damage and melanogenesis, and potentially inhibit antagonist microbes.

It is essential to develop a comprehensive understanding of Malassezia yeast′s interactions with the skin under normal and pathologic conditions, such as a) commensalism (as observed in normal skin) as there is lack of evidence of a mutualistic relationship between Malassezia and skin, b) changes in melanocyte function that causes hypo- or hyperpigmentation without visible inflammation (pityriasis versicolor), c) inflammation without evidence of a influential adaptive immunity response (seborrheic dermatitis and dandruff) and d) induction of specific immunity (atopic dermatitis).

In pityriasis versicolor, two facts support the role of Malassezia: (i) a frequent positive culture in the lesional skin and (ii) the presence of a hyphal form, independent of the Malassezia species isolated.

The putative relationship between Malassezia and seborrheic dermatitis is clear as the antifungal administration results in clinical improvement of seborrheic dermatitis. Malassezia globosa and Malassezia restricta are two of the most frequently isolated Malassezia species in this disease. Also, robust evidence shows that individual predisposition and host-Malassezia interaction, in addition to the mere presence of Malassezia, are essential in seborrheic dermatitis. Environmental factors such as UV radiation and antagonistic microorganisms may induce physiologic stress on Malassezia and the skin, modifying the immune system, individual susceptibility, and yeast metabolite production and triggering and perpetuating inflammation in seborrheic dermatitis. Topical application of oleic acid can induce desquamation on nonlesional skin of seborrheic dermatitis patients. 

Evidence proves the presence of Malassezia species in psoriatic lesions; however, epidemiological data on the distribution of Malassezia in psoriatic lesions is still inconsistent. The benefit of antifungals in psoriasis is still contradictory. They may be beneficial in scalp psoriasis resistant to other topical or systemic treatments. 

Although the role of Malassezia in most dermatological disorders is still unclear, evidence has proved it. The mechanism by which Malassezia induces different immune responses, and hence different clinical manifestations in different diseases, still needs to be solved. Further investigations are warranted to clarify the role of Malassezia in dermatological disorders and the potential of new treatment approaches.

Source: Kurniadi I, Wijaya WH, Timotius KH. Malassezia virulence factors and their role in dermatological disorders. Acta Dermatovenerol Alp Pannonica Adriat. 2022;31(2):65-70.