In brief

Although dandruff is classically associated with scalp colonization of Malassezia yeasts, bacterial and fungal shift can be observed also, in individuals with dandruff, in non-lesional sites such as the forehead. This finding suggests that dandruff is related to a systemic process that is not restricted to the site exhibiting clinical symptoms and that individual undergo systemic alterations, which could be considered for redefining therapeutic approaches.

Introduction

Dandruff affects approximately half of the world adult population. Dandruff is an inflammatory chronic disorder related to skin barrier disruption, epidermal cellular proliferation and differentiation, as well as shifts in gene expression patterns and in cytokine and lipid production. Dandruff is characterized by scaling, itching and sometimes erythema, on scalp. Dandruff has been frequently associated with a proliferation of Malassezia yeasts, which are also members of the healthy cutaneous microbiome. However, little is known about bacterial and fungal microbiota associated with skin from healthy and dandruff subjects and between lesional and non-lesional skin sites.

Bacterial and fungal microbiome from healthy and dandruff individuals

In both healthy and dandruff individuals, Propionibacterium, Staphylococcus and Corynebacterium are the three most abundant bacterium genera and Malassezia restricta is the most abundant fungi. At the genus level, healthy bacterial and fungal communities clustered according to body site, indicating that scalp and forehead from healthy individuals harbor distinct microbiotas.
Dandruff is related to dysbiosis in both clinically involved and uninvolved skin sites. Indeed, in dandruff individuals, the microbiome differences observed between lesional site (scalp) and non-lesional site (forehead) are similar to those observed between scalp and forehead in healthy individuals (Figure 1). However, the diversity of the Malassezia community, at species level, was not associated with dandruff. As, well, no Malassezia species was overrepresented in dandruff subjects, either in scalp or forehead samples.

Figure 1. Average microbial dysbiosis index for bacterial communities according to health status. Significance was determined by Two-way ANOVA Test. Bars represent Mean ± SEM. ****p < 0.0001.

Conclusion

Dandruff is associated with bacterial and fungal dysbiosis even in nonlesional sites, such as the forehead. The process associated with dandruff might be systemic and not restricted to the skin site exhibiting symptoms, although the non-dandruff site studied here is the forehead being close to the scalp.